Later engines from the factory seemed to have had the intake sized so that they could use the new AMAL 932 carburetor. This would have had a 32mm throat size. Based on measuring up the heads I have available that works out. However racers always try and get an edge so the AMAL Mark II I have is actually a 34mm on the intake manifold side and 43mm on the air side. This may or may not present a tuning challenge. Since it's more normal, getting the engine to run well with the know quantity of the AMAL should prove to be simpler.
I got one! I have luckily, for the ever curious part of me, been able to score a POSA Fuel carburetor of 32mm. Even better yet it came off a light sport airplane and has had a fuel mixture control added. Now I have a simple but reputedly enigmatic carburetor to eventually play with and either be successful or frustrate the hell out of myself. No matter what happens it will be educational and there will be something learned.