blocks themselves-- mostly very small differences such as the size of the oil jets that go in between the block and heads. If you have an earlier block you can still use with later heads. Also, depending on the heads you use it dictates which plenum setup you need and which injector rails you can use. Once installed its nearly impossible to tell which setup you're using (earlier vs later heads and plenum).
Don is almost always correct, but I think he forgot some subtle details about this. 96 also has other differences (outside of block) due to the OBD-2
