Hi Ross
Just seen this thread , ive been running a Electrex for 9 or so years, i converted it to run a wassell about 4 years ago.
My electrex is 3 phase , same as yours ( they used to do a single phase version) but running a "master igniter" cdi/coil.
From memory, the original set up was run as a single phase ac system . leaving aside the ignition/cdi side, mine had 3 yellow wires, 1 was blanked off , 1 was earthed and 1 went to the small regulator.
To convert to wassel i just connected the earthed yellow and the reg. yellow, to the wassell , much the same as you would do with converting a "normal" stator to a wassell full dc system.
You can buy a 3 phase wassell , it has 5 wires instead of 4 , and you use the 3 yellow wires connected to the 3 on the 3ph wassell . This was going to be my next step some years ago , but tbh it powers enough for me so i havent bothered

Electrics arnt my thing tbh and i have no idea if its a "true" 3ph system ....or even if 3ph would be better than 1ph
Russ