I just picked up a longblock 305 for a rebuild to replace the junk engine in one of my birds.
The donor came from an 88 truck and it's going into a 91 bird.
The only major difference that i've noticed at the moment is that the balancer on the truck is 1 1/4" deep from front to back whereas the balancer on the bird is 1 3/4" deep. Not the snout but the part that the timing mark is on.
Which one should I use? It doesn't look like the original bird balancer will fit the crank fully seated without rubbing on the timing chain cover. With that in mind, are all my pullies going to line up if I use the truck balancer?
The timing marks are also in different locations yet the timing tabs on both covers are in the same place.

 

Verify the marks on the truck balancer line up with the timing tab at TDC.
If the balancer and timing cover are original, I would leave them on.
The surface that the pulleys mount on is a standard distance. Alignment won't be a problem.

 

Judging by the "clean" marks on the balancer where the front seal rubs I would agree with you on the alignment issue.

The interesting thing is that the timing slot that's cut into the balancer is in a different spot when compared to each other. I'm going to have to figure out if one of these balancers has slipped.

 

GM changed the location of the timing comb on the timing cover a few times, which means there were corresponding changes in the TDC mark on the balancer.

 

Both timing covers have the tab in the same location. The balancers timing marks are in different locations. I'd say they're about 20 deg different.

 

One of those engines had the wrong balancer then.

 

I'll be using the truck balancer.
It actually looks like the same balancer that's on my other 3 birds and the timing mark is in the correct location compared to a new one for the bird.

I guess i'll dump the one that came on the firebird. I will still verify TDC before dumping it though.
Thanks for the help.