1998 Johnson 30hp lower unit search, which years interchangeable

I bought a nice Carolina Skiff J16 w trailer for i think 900 bucks or less. It has a center console with a 30hp johnson. I was able to get the engine running easily but the lower unit was locked up. I am looking to swap the lower unit (short shaft) from salvage or buy a spare parts motor. I found a 1991 which the owner thought was a 1998 but when i looked at the tag ended in 91. The engine had 85psi cold he was asking 1000. I think it was low compression although it might have been dry since had not run in some time both were 85psi. I told him i could only give him $400 because salvage will give me one for 550 pressure tested for a lower unit. I think a 1991 will fit a 1998 . I was wondering what other years will work? His lower unit oil was black but i think it was good and i could possibly use coils and other parts off the top end even if the engine is bad for $400.

Thanks,
John

Anything from about 84 and newer 20 / 25 / 30 hp 2 cylinder will fit.------------In my area I pick up parts motors for about $200 or less.------------Bad power heads with possible good lower units.