I had the same problem w/my 250... loosining flex plate/flywheel bolts dampers coming loose, chewing up the front of the crankshaft where the damper goes.
I tried every thing... almost. I rev above 6000 RPM keep in mind.
The only thing that worked for me was I installed an 8 inch SBC damper.
Let me tell you... what difference it made!!!
Since then Flex plate bolts do not come loose, the damper has not had one problem & now the engine turns RPM quicker & higher w/the V-8 damper.
I just had to move all the accessroies forward to line up the belts.
Goodluck!!!
Hank
