I ended up drilling and tapping the end of my crank shaft to accept the 7/16x20 f100 flywheel bolts. It came out perfect. Now I’m working on my clutch pedal assembly. I found a 79 Mustang assembly for $20. I ground the weld off the shaft end and separated the shaft from the pedal. I put the shaft in a lathe, turned off the threads, drilled and tapped the end to 5/16x18 and attached a modern BBK billet quadrant. Turned down some spacers to get quadrant and clutch cable alignment and fastened it together with a hardened shoulder bolt. Assembly is ready to media blast and paint.
2020 and this thread is still being used. I’m doing the swap NOW on my 87 T-Bird 3.8. The 83 F-100 flywheel.. The bolts I bought to bolt the flywheel to the crank are a no go. Those bolts are about .430” and my stock bolts are about .390” and different thread pitch. So, I need to find a bolt that has the .430 shoulder but .390 thread. Yay.. Off to O’Reilly with 2 bolts and some calipers. Anyone know the answer already?