3400 V6 - differences between 96-99 versions and 2000+ versions

I know the changes aren't major, but I'm wondering what exactly changed in 2000 on the version of the 3400 SFI engine used in the Venture/Montana/Silhouete, Grand Am/Alero, Imapala/Monte, etc.
I seem to remember reading something about revised heads, and perhaps some updated emissions stuff, but the specifics escape me. Do any of these changes render the newer 3400 unusable in models that used the previous 3400?
I'm looking into dropping a low mileage used 3400 into a 97 Trans Sport; and I'm wondering if the 2000 and up version will be a direct drop-in, or if the 96-99 version is the only one that will work. Specifically, would using the newer 3400 require a new ECM, or will the 97 work? Are there any new sensors to worry about? That sort of thing.
http://www.3400swap.com/ has a "how-to" guide for swapping a 3400 in place of a 3100 into a 94-98 Grand Am, and it seems to suggest any version of the 3400 is more or less a drop in for the previous 3100 SFI (and presumably the earlier 3400 SFIs), but any insight would be greatly appreciated.
Thanks for the help.
-Bryan
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