One of the issues that people often seem to overlook is that we tend to lump all box type pipes into one category, which is no more realistic than talking about 'fitting an expansion' as though all expansions return the same performance across the rev range, which clearly they do not. Indeed, fit a genuine Taff Road pipe to a TS1 and you will have a completely different peak power, completely different peak revs, completely different powerband range and completely different gearing requirement than if you had fitted the same motor with a JL4, PM, some of the Kegra pipes, etc. The same goes with 'box type pipes.
It has made me snigger to myself when people have been pointing out just how well/high some box type pipes can rev, suggesting that many box types can rev further than many expansions. Yes, that's true, but many expansions can rev beyond other expansions, and many box pipes rev a mile beyond other box pipes. We really do need to stop lumping box pipes into just one category... unless you are prepared to consider all expansions as being the same too.
Holty has already mentioned the excellent TS1 performance offered by 'SOME' of the VW options out there. Indeed, 20 or more years ago I was loving the power delivery of my straight through AF 48mm VW clubman on my TS1, however, the noise was extreme and I got stopped a number of times. This prompted me to go back to AF and ask them to do me a standard tailpipe type (slightly larger diameter) version of the same. This was in the days before Indian AF clubmans and was made in the UK. The pipe fitted beautifully... but the pipe restricted the revs so much that the pipe called it a day on revs before the TS1 even started to get into its stride., converting a previously great ride into something completely underwhelming. Missing the powerband by 1000-1500 rpm is the same as missing the power by a mile, giving the sensation of always being in the wrong gear and 'hitting the rev wall/ceiling' just before it comes to life (like riding a standard P-range... you just can't rev them).
However, things have changed in more recent years and the work that was put into developing a new breed of 'super clubmans'. Personally, I saw things start to change with the Ancillotti that came out for early Imola use, which as a mini TS1 needed to reach the revs that the kit's porting wanted to work at. Saxelby already had a well respected clubman that I'd put into this category, which allowed some of my iron motors reach a slightly higher rpm powerband than some of the other generic clubman pipes simply couldn't reach (box type but certainly not to be thought of in super clubman terms). However, my Ron Moss clubman pipes, of which I own 2, took the performance of these same motors to a whole other rpm and performance level, with my tacho indicating at least another 1000 rpm over rev on the same Avanti TT3 and Mugello 260 motor that I ran them on... noting that noise level made me change the TT3 to a Fran Supertourer but the Moss clubman is still on my 260 and rides like a dream.
One thing to note is that the Mugello 260 was initially intended to run on the 48 standard tailpipe clubman that I mentioned previously (AF but pre Indian clubman days), however, this caused a gradual heat buildup in the pipe as it simply couldn't shift enough gas out quick enough. This showed frighteningly on my EGT gauge and was terrifying to watch on Readspeed's dyno as the U-bend changed from cold to cherry red, then beyond to bright orange!!!!!!!!! Yikes! No fueling, compression, porting or timing changes could stop this, however, the bike changed the instant that I changed the pipe to the old straight through VW, later changing to the Moss clubman. Please note that my EGT and tacho use allows me to swap configurations and see very obvious changes in return from one configuration to another, rather than trying to judge by ear, feel or variable (!) Lambretta speedo alone
The last decade's clubman development, designed and revised with the benefits offered by dynos, mirrors the last decade's expansion development. By that I'm not suggesting that the performance is the same between all box pipes and all expansions (FAR FROM IT) but people would very quickly argue back if someone were to suggest that all expansions were one and the same... and so it should be for anyone suggesting that box type pipes are the same. Rather, box type pipes have a MASSIVE range of performance, from power spread to rev ceiling (and noise!), along with all the same issues of quality, fit and ground clearance that we find in expansions too.
We also need to bear in mind that the spec of the motor (cc and porting spec) has a massive influence on suitability of pipe. Some revvy pipes will never reach their powerband as the cylinder's porting cuts in as the rev limiting factor prior to coming onto the pipe, and some revvy motors will never reach their cylinder's porting power as the pipe is the rev limiter before the cylinder reaches the revs it needs. In both of these cases it is neither the fault of the cylinder nor the pipe, rather the fault of the builder that opted to use A with B.
So, what will probably work in this case? Well, as Holty touched on, I have no doubt that my 48mm straight through VW clubman would work perfectly... however, a 48 VW based on one of AFs current clubmans would kill it straight away, unless it was completely gutted and reworked internally.... my VW would also put your neighbour's windows through (I kid you not!). A Ron Moss clubman would almost certainly work, which is supported by a number of people running them very happily on TS1s, including on a couple of bikes used for Euro Lambretta long hauls and my pal Bruce running one on his Taffspeed tuned TS1 that he rode to IoM with me a few years back. NB that both of these 'box type' clubmans do not restrict flow out much but that they also let a lot of noise escape too, so much that I have had to take them off various motors of mine, which otherwise rode wonderfully and reliably. When noise reaches these levels then I have to conclude that they have 'failed' to perform on this factor, however, the same pipes are not too loud on motors with smaller exhaust ports. Personally, from experience of running my standard tailpipe RS clubman on my TT3 and 260, I'd suggest that this might not work too well on the suggested motor, yet this pipe has been a wonderful performer on an iron 225 and Rapido 200, both configurations that I've rallied on. MB/BGM super clubman... not sure. I've got a new one sitting in its box but the frequency of issue at last year's Euro has made me think twice about fitting it (NB: Scooter Centre have changed manufacturer and this should no longer be an issue) but the performance of earlier versions has put it into this super clubman bracket... but from what I've seen/heard I would put it somewhere between the RS clubman and the Ron Moss clubman as far as ability to rev on to the higher revs that many of today's ported kits need to reach to operate correctly.
Box pipes are not all the same... nor are expansions.
Adam
PS - Sorry for the waffle and sorry that I can't muster the energy to proof read / re-read the message above

Cheers all.