I can't remember up until what year big blocks or GEN's fit. A guy I know has a 454 out of an RV or motorhome, 90 or early 90's 1 piece rear main seal, spun bearing, standard bore, complete w/ everything except the heads, couple hundred bucks..... bad news or something to look at?

I remember reading that the Gen V started in 1991, I think. They did not have the boss for a Mech fuel pump (would have to use an Electric pump). They also do not have the threaded boss for the Clutch linkage (Man Trans). With a spun (rod ?) bearing, your looking at least a new crank and rod. I'm not sure what else is different, maybe other will have more input.

Fred.

I gave up on getting a good MarkIV block and have a new/near new GenVI block now. You can use the older style crank in the new blocks by installing a $90.00 2 pc. crank seal adapter. A '91 block is a GenV and will need to use heads from a GenV or GenVI, whereas, a GenVI (1996? & later) can use either the new style heads or the old style. Either way, you can get parts for all of them very readily. If you don't mind the electric fuel pump, build the GenV motor. GenV's are 4 bolt main and most likely shouldn't have 30 years of corrosion in the water jackets. For a couple hundred, I would jump on it.