Sorry, I meant carrier = FMC carrier == base board == KC705 and such (NOT carrier frequency)
Your adapter is then a 4 FMC (for the FMCOMMS2) to 2 FMC - board correct?
You could make it work on multiple carriers - just be mindful of the available pins (not all are populated).
I wouldn't worry about the pin assignments or clock regions.
Always use 00_CC for clock, and stay within 01 to 16 for a single device.
You can take a look at the ML605/PA project - it is not fully tested.
As we mentioned before, it is just that the Vivado frame work can not support a direct XPS-only flow.