The early 289/302s had the same imbalance as the 351 so you can use flywheels and balancers interchangeably but the later 5.0 had a different imbalance so you must use specific parts. The 351 was never updated to the newer imbalance so even the last 351s still used the 28.5 ounce imbalance of the early 289/302s as opposed to the 50 ounce imbalance of the late model 5.0 engine.
the 302 went to 50oz. balance in 1980 the only difference between the 28oz. is that the early 69 and below(i think that was the year) use the 3 hole pully setup