308 is great travelling ratio to keep revs down it is better if you 253 runs well like extractor ,4 barrel carby and manifold and if you are rebuilding a motor have it balanced to get best hp
As for beleiving the stamps on the yok seal cover I have been caught out by this by selling a diff for $100 dollars to purchase another for $450 only to find out that the one I sold had a 308 crown and pinion
If you take the rear cover of It is stamped on the crown wheel some where it is pretty easy to find