I'm resurrecting an old post to provide an update on what finally happened.
It took me 2 years to get to the point of actually installing the heavy duty flywheel. The actual installation was easy. It fit onto the crank perfectly and bolted easily. Adding the new clutch was fiddly, but I managed. The issue came when I tried to install the clutch release fork. It would not fit between the stud and the new clutch cover. No matter how I tried to wiggle it past, it would not fit. So I went to the engine that I had recently removed from the truck and looked at the clearance between the stud and clutch cover there. There was a significant amount of additional space on the old engine.
I tried to measure the thickness of both flywheels and it appears that the heavy duty flywheel is much thicker than the regular one. On the order of about a 1/2" thicker. So now it seems as though I'm going to have to remove the clutch and heavy duty flywheel and go to the original one, after getting it resurfaced and replacing the ring gear with a 12V ring gear to match my starter.
The other issue was the pilot bushing fitting into an original powerglide equipped engine. I did buy the recommended bushing. When test fitting the bushing, I found that the one that came in the clutch kit was a better fit to the transmission input shaft than the extra one that I bought. So I went with that one. It was an extremely tight fit when installing it into the crank, but it did eventually seat all the way.
I'll add some pics of the clearances between the stud and clutch cover and one of the pilot bushing after installation. The clearance pics are kinda hard to see, but better than nothing. In the pilot bushing pic, I had not yet removed the old powerglide flexplate when I took the pic.
