I guess they redesigned the motor a bit, with bad results. This reminds me of another change at around that time. The factory went to a smaller crankshaft flywheel mounting register (is that the right word?) I only read about that years after I had been running a large hole 67' manual flywheel behind a 76' 350 with the small register. I didn't realise I had done that until I went to remove it and it just fell off. Supposedly that should have been a catastrophic failure but I had no problems after 8 years of abuse. So if you get a 76' and up motor, try to get the flywheel or flexplate that belongs with it.
