Ford never used a zero weight for the small blocks. All 5.0's through 1979, and all 351W's use the 28 ounce flywheel and balancer. All 5.0's from 1982 on used a 50 ounce flywheel, and a 34 ounce balancer (but everyone refers to that as a 50 ounce balancer so that people don't get confused.
). However, the size of many of the 351W and 5.0 28 ounce flywheels were different.