With your porting skills

I'd suggest you need look no further than an over-bored OEM barrel -or an SR type barrel if you have many hours & patience - with a piston to suit from the Grampian catalogue. With a wise crankshaft selection, preferably longer stroke, longer rod & packing to suit, you can dial in your desires.
Air filtration is the civilised way to go, but @ the very least a better, more capable elbow/bellows will be in order. You might get away with a re-engineered OEM filter box.....
Carburation? Aha! PWK are filter friendly & do not cause hot start issues. They need checking out/blueprinting like every make of carburettor, but they are a joy to work with IMO.
The exhaust may as well be a DIY clubman. That way you can control the ''U' pipe & tailpipe sizes & even AV mount.
Retain points ignition (for reliability

) but go for a 'J'/Luna flywheel on a GP boss. Screwed on, not riveted......the boss will take an M6 tap & buttonheads are neat. Upgrade to 12 volt though. Do you know any good Sparkies?

Is that an oxymoron?
A mate built a 200 engine along similar lines. He even set ignition @ 21 DBTDC. It was an absolute joy to ride.
Front brake? Well, what DON'T you know about inboard discs? Though a TV175 S2 drum brake would suit