Two major revisions.
All Renix and HO up to 99 are similar, and you can bolt any manifold to any head. However, the renix motors have an EGR line that threads into the collector. To keep the EGR, you would have to weld a bung onto a later mainfold.
They substantially revised the exhaust port shape on the '00 head, and the manifolds don't fit the earlier heads(They'll bolt up, but won't cover the port.)