If we have some UDT-incompatible selfish preferences, that's fine with me - so most likely this is so different from Rawls that it's not even a fix to selfishness.

But yeah, the peace and harmony model is quite Rawlsian, and is somewhat equivalent to the claim that if we want to self-modify, we should also act as if we self-modified in the past. (Where there is some vagueness in how to cash out 'past self', which probably makes the UDT formulation nicer).