differences - 79 to 82 258's

The engine design changes actually occurred in the middle of the 1980 model year, sometime in calendar year 1980. So you can have a 1980 model with the older, heavier 258 OR the lighter one. The easy way to tell is the heavy one has a cast iron intake bolted to the exhaust manifold. The light weight model has an aluminum intake and a totally separate cast iron exhaust manifold.

Changes included a lighter crank with fewer counterweights, smaller headbolts (7/16" vs. 1/2"), a slightly lighter (thinner) block casting, and the aluminum intake. IIRC about 60 pounds was shaved off the engine. No changes were made in the external casting, so it looked and fit the same as always. The casting was changed to the same externally as the 4.0L in 87 (with the exception of a provision for a mechanical fuel pump I think -- or do 87-89 Wranglers use an electric pump??). The block is about 1/8" wider, but that's the only change. The 87-89 258 block is a different casting than the 4.0L block -- it can't be bored 0.105" over.

Roughly 80% of parts interchange among the 199/232/258/242 (4.0L) engine family. Cranks will interchange as will rods. You must use the right piston for the length rod and stroke crank used. Heads will interchange. Use spacers or step dowels to put early or late heads on mid 80-86 blocks, or ream and tap the block for 1/2" head bolts. Ream the holes on a mid-80-86 head to stick it on an earlier or later block. Most things interchange, but there are some caveats. If you use a 4.0L head you must use a 4.0L exhaust manifold. The aluminum 258 intake will fit, but you have to adjust the alignment dowels or take a lot of care when lining it up (almost impossible with one person and the engine in the vehicle). So you do have to be careful! The 4.0L crank nose is slightly shorter than earlier engines, but that's the only difference (other than stroke). I have a 1987 4.0L block and head, 1974 crank and rods, 4.0L replacement pistons, 1979 timing cover, and 1974 engine mount plates and oil pan on mine.