232 upgrade to 258?

So I guess there was at least two different intakes. I sure wouldn't have made two!

Yes, the Jeep oil pans are deeper, so you'd need the pickup tube as well. He'll also need a 258 oil pan... maybe.

Wizzle, look on the left side of the oil pan where it's close to the block. Is the pan smooth, or are there some "bumps" along the side of the pan? The "bumps" are there to clear the 258 rods. I believe AMC made only one pan, but that may have only been for the last few years of the 232.  If you have the "bumps" in your pan you can use the pickup tube and pan from your engine. If not, you might be able to dent the pan with a hammer to clear the rods rather than ship one over. A 4.0L pan and pickup tube will work to, I think. Those you can find over there.

What about a 4.0L from an XJ?

Why the 258 sump? Economics. Same sump bolted to the 232 and 258, why make two different ones? The bumps on the left side do noting in the 232, but do no harm either. That's why I questioned the two intakes, but AMC may have used two different suppliers anyway, or they made enough manual steering cars that the 3-5 cents of aluminum for the PS mounts made a difference to the bean counters... or maybe the engineers just didn't like the looks of bosses sticking out on the intake with nothing attached. The sump doesn't easily show like the intake does.

The only way to determine if you have a 258 is to measure the stroke. Get a piece of stiff wire and run it in a spark plug hole. Run the piston down to the bottom then mark the wire. Run piston to top and mark again. Make sure you use the same reference point when marking. Measure between marks. Is it closer to 3.5" or closer to 3.895"? Shorter is 232. Your measurement should be slightly more than the actual stroke due to the angle. If the measurement is anything less than 3.895" it's a 232. The 258 will measure right at or over 4" using this method.

You are correct, pre 1979 casting numbers are shared between the 232 and 259. I found one  casting number in my list that is in the 232 section that isn't in the 258, but that is likely a mistake -- it is probably a 70 only number, or should be in the 258 listing also. I have it listed as 70-72, bit it can't be over that range since the 71 block is taller. But then some of the short blocks were likely still cast for a couple years to allow for warranty replacements. If a block cracked or was otherwise damaged in a new enough car the internal parts would be changed over. Makes no monetary sense now, but back then the dealer and/or factory probably saved a bit by doing it that way. Labor costs in the US have skyrocketed until it's not worth the effort any more, that tells you something about how labor costs have gone up right there!