I'd think the National Simulator Program Office in FAA Atlanta would be a good place to get the authoritative "what you can and can't do" answer for a given simulator/aircraft (though they won't tell you what the 737 did, they'll tell you what you can, and must, do).
(Obviously that's not much use if you're looking for a JAA?EASA qualification)
The process certainly seems plausible; we've used a similar approach of demonstrating 'similarity' between two models of the same basic airframe to allow two types to share some or all of the basic QTG. Even if you can't get away with no new QTG testing, the saving on what I'd call 'development' testing for a similar type can be considerable (the tests you need to construct the flight model to a decent fidelity, which are usually rather more than the qualification minimum required tests)