[Jac Mac]

Dean,
Not uncommon for that dowel to only be a very light push fit--varies from cam to cam in my experience ( coming up to 40 years now ). Find an old 289/302/351W cam and steal the dowel out of it.

I would just get the new longer dowel or even just cut an 1/8" long piece off a 5/16" bolt to stick in the hole before fitting the existing dowel, though given that its had a bit of pain recently your probably best to bin it!

Two Piece eccentric- assuming the cam gear does not have the raised lip on its front face you will have to make up a washer to fit between the inner part & the front of the cam gear that is slightly thicker than the outer ring in order that it can rotate as designed when its all bolted up. This washer will also require provision for the tang that fits into the dowel hole.