i've read all the threads i can find here and other sites and it always seems to come back to this
so,
1: no matter what you need to cut the upper support out and redo how you stiffen the floor area
2: using the US Cartool piece just means one less thing to fab
3: in general you want to keep the drive shaft angle as close to factory as possible, even if that means cutting the floor.
4:whether a 500 also needs the floor cut to fit in there is still a question