Yes, there are differences... actually there are more head revisions than there were year models and there are a few different block revisions as well. The later revisions are said to flow better and I think they had more vanes. I've never heard anything about them really gaining anyone more power though, but I'm sure there's a TINY amount to be had from a newer revision head.
They are all interchangeable though. The only thing that would need to be changed is if you're swapping from a GTE to a GE or vice versa; You'd need to swap the intake cams them and reshim... of course you should reshim for proper valve clearances anyway, it's overdue I'm sure.
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