The balancer on ALL '81 and up 5.0s is the heavier,50 oz. rather than the earlier 28.4.The number on the bal will be E4TE-..... showing that it's spec'd for the '84 Truck Engine.All you really have to do is check a few things on the block- the casting code; E7AE showing that it's an '87 up block,and if original and un-machined then DEFINITELY a 50 oz roller block.Either that or;if you've seen into the lifter valley and can confirm that it's a roller block,or check the serial # stamped into the block at the back of the intake.If the 6 digits match your VIN then again you know for sure the thing's a 50.
If the flywheel came from a 1980 or earlier it's not gonna work,so go get an exact replacement.They sell new for around $100.00 us,so it's not even worth finding a used one,getting it turned,etc.
Changing the balancer to an earlier one won't work,and in fact could trash the motor completely,as it's the CRANK that is balanced with the flywheel and balancer.If you ever have a motor apart,look for the casting code;it'll read 2MA on 28.4 oz cranks and 2MAE on the 50 oz.The two are NOT interchangeable unless the other parts are changed as well. | 
28oz and 50oz balancers, which do i have? 
I have a 1989 5.o that had a aod behind it now I have a T5 installed and I now have a high rpm vibration. how do I know if I have the right comination of balancer for the flywheel. The flywheel came from an earlier 5.0. are there any markings to distinguish which one i have? how do I tell which balancer I have? Thanks Ron
