Bill on the GMC I don't believe you can install one...the design is all wrong as the sealing surface for the GMC is down on the shaft (before where it meets the flange) and in the Chevrolet it is up on the flange itself so the seal for the Chevy is longer and just different. I think on the GMC all you could do would be to have that area of the crankshaft polished. But fortunately the GMC does have an oil slinger (which I have felt for a long time the 235 needed). Jerry (HotRodLincoln) has built a jig to allow the Chevy block to be machined to accept a one-piece seal using a portable boring bar approach and we've been discussing other ideas about how this same procedure could be turned into a drill press approach. The problem is you can't find those old seals made with asbestos so easily anymore. Since the late 70s they've been banned.

On the GMC I've not figured out how to use a one-piece seal, though. You'd have to remove the flange and machine it so that it would attach back using bolts and dowel pins and man...that would be a lot of work and $$$.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end