What brand of clutch were you planning on going with? I was looking at the Quarter Master V-drive 7.25" units, they don't have a flywheel, but the triple clutch kit isn't much more than a regular single plate clutch. The only hard part is the flywheel and the throwout bearing. I don't recall what the R154 spline count is (I have the info at home I think), but from what I remember they had one that would work.
I was also curious if you could simply use the flex plate from an auto with a flywheel mounted "on top", allowing you to make the flywheel outside diameter only big enough for the clutch disc/pressure plate mounting while not having to worry about attaching a ring gear to the custom flywheel.
edit: found it, spline is 1-1/8X21