Hard to describe the differences, they are subtle. Check the casting number on the head, underneath the intake manifold. I can't remember where the ones on the block are, but that will tell you.
An I head swap should be revving to the I redline at 6250 if I remember right? I would sort that car quickly. Sounds like a half-finished swap. Post pics, and look at the number on the DME in the top of the glovebox.