counter weights
 

How can I determin if the counter weights, front and rear, are from an 89-91?

Part numbers.

No realy? problem is, that I have a bunch of them without part#'s on them smart ass. I'm looking for visual clues...

Aren't they the same?
Did you do a search?

s4 and s5 counterweights are different.My s4 counter weight has only one hole drilled into it.Weigh them and see if they have a different weight to them.Because they all look alike visually.

The counterweights are visually identical. The holes drilled in them mean nothing in terms of determining which years they are. The '89-'91 counterweights are lighter than all the earlier ones but only very slightly. It would take a postal scale to see the difference. I had this scenario several years ago with 2 different counterweights during a rebuild. I flipped a coin and hoped the engine wouldn't shake when started up. I got lucky. Unfortunately I don't really have anything helpful to tell you.