there are internal differences between your 86 na and the 4agze engine. the block, crank, rods and pistons are different. your na rods are not interchangable with the 4agze ones, unless you change the whole crank over for instance.
if you had a later 7 rib 4age then the only internal difference would be the pistons and no threaded hole in the block for the knock sensor (which can easily be drilled and thread tapped).
not sure what you are trying to acheive? if looking at building a boosted engine keep the 4agze under wraps in your shed until your ready. if looking to stay na, the early 3 rib is the go with it's lighter internals.
