72 Demon slanty-to-340 Resto

To shift over to looking ahead at the trans work, was wondering what thoughts would be on this article 1969 Dodge Dart - Mopar A-Body Tech Easy 6-Speed Manual Swap

Found this on American Powertrain's site 1967-76 A-Body Pro-Fit 6-Speed seems it's a popular enough swap to warrant a kit. Might make the swap easier?

On the other hand I was also wondering, what separates the current Tremec T56 from the T56 that was in the 90s Viper? Other than it was originally developed by Borg-Warner then carried over to Tremec? Because I heard about a guy up in Portland selling a few low-mileage Viper transmissions for $1700 a piece, I'm still a ways away from that pricewise but if they're reasonably compatible then I could just try to source the right parts and go the cheaper-but-harder route. That'd cut down the cost of buying a brand new kit with a T56.