You could also buy 3 of these:
https://tinyurl.com/mpn8fwda and then build simple adapters to let you mount each one right straight on the 235 cylinder head. The size looks pretty doggone close to what you'd need anyway (1.5" diameter as I recall).
Each one of those has been engineered to supply 40 cubic inches and since no two of your siamesed cylinders will be firing sequentially, you'll be good to go. Get a common motorcycle 1 into 3 cable for the choke and throttle and also hook it up to the accelerator pump. A little fiberglass to build a 3 dock fly looking air intake using a common air filter like the Chevy Blazer and you'll be ready to go.
Oh, one other thought. These were designed for simple gravity flow fuel supply so you'll need a very low psi regulated electric pump, won't you? Sure...maybe 1.5 or so psi. Or you could gain some extra room and preserve the gravity flow scheme by mounting your gas tank on top of your cab. Or wait just a doggone minute. That room between your headliner panel and the top of your cab? That wasted space will become your new fuel tank and you can simply run a fuel line down through the roof pillar and into the engine compartment. And they thought I was sleeping in those industrial arts classes.
