I believe the biggest differences were the position of the trigger group and where it attaches to the main tube and (if I recall) the breach block attachment to the tube. The pressure tube, breach block, trigger group (I believe) and stock are not interchangeable between the two generations. The valve, guage block, fill assembly, barrel and most o-rings are interchangeable. There may be other differences I've forgotten and I might be mistaken about some I've mentioned. For a definitive list of differences, the parts list of both generations should be consulted. Parts with the same part numbers are interchangeable. I know for a fact the valve is interchangeable between the two, as I have a generation 2 valve in my generation 1 Marauder.
As far as the need to know which version you are dealing with for the TSS, that will be due to the trigger group position, which also means that the hammer and sear engagement are different and require slightly different parts in order to work correctly/safely.