Right, the heads are different; the biggest thing there is, the intake ports are in a different place, moved upwards about ¼" to give the port a straighter shot at the valve. There are some other detail differences, like the chamber shape and the bolt patter; but the port relocation is the biggie.
ANd of course, the motors that came with those heads, all have the "central port" fuel injection, with the "spider" thing and the poppet valve and all that; and a crank-triggered spark.
Other than those things, there's not alot of differences. Block is the same, pistons are the same, cam is interchangeable except that they finally switched it ro a roller in 96, external bolt patterns are all the same, etc.