[RHINO]

hereare a few of my thoughts,

balance, the engine must be internally balanced, i have both flywheel and flex plate in my hands and there is no weight on either, the flex plate has nothing and the fly wheel has a few holes drilled to balance it to itself.

adapter, a spacer style already exists, not my first choice but it does work fine and has been around for some time so it is proven. its what i have, two flywheels gets a little heavy but my chevy flywheel is only 14lbs and thats about the difference from the isuzu pressure plate.
how about this? have the isuzu flywheel re-drilled to accept a cruiser pressure plate, simple and cheap, then have a bellhousing made, could get costly. for this i would contact the lakewood company and talk about a stamped steel one.

flex plate, no go on its own. it needs something bolted to it like a converter to keep it rigid otherwise it warbles and flexes while being turned over.

also, is your machine shop able to balance a custom spacer, flywheel or whatever spinning thing you get made? its very important they can.