got a free engine, need help

Got an old jeep striaght 6, and the person who gave it to me isnt sure if its a 258. Its been rusting away in a barn forever and its out of an early 70's cj. Is there simple way to just measure the cylinder bore to see what size it is. I ask this because i know w/ a chevy smallblock, if your not sure if its a 350, you just measure the cylinder and see if its 4.00" or whatever size it is to identify it. I cant run numbers because its so rusted. I just need the thing for the crank and rods. Any help would be awesome. Thanks

The old AMC I6 was available as both a 232 and a 258, and they had the same bore. The difference was the stroke, so you will need to measure both.

232 (3.8L) ==> 3.750 bore x 3.500 stroke

258 (4.2L) ==> 3.750 bore x 3.900 stroke

Thats exactly what i needed to know. Thanks a lot. Looks like i got me some stroker parts now. Anyone want a 258 block, head, and intake?