Originally Posted by 302xm
They most crittical change they did was engine balancing going from a 28oz harmonic balancer to a 50oz balancer due to heavier conrods which must be taken into account when mixing parts
Are you sure about this, the rods are nearly identical from 69-96 as I am using 96 rods in a 69 block.
The counter weights on the crank changed in 85 (roller cam), that is when they changed to a 50oz balancer.
Flex plate/flywheel and harmonic balancer are the important ones to watch out for; pre 85 had 28oz balancer.
Earlier engines 289HP and 302 Boss used a heavier harmonic balancer for the heavier rods used, but it was still 28oz counter balanced