I don't know what size for a rear mount, but I have a pair of TD04-13G turbos off a Volvo for a similarly sized engine.
Looking for 8-10 psi, similar operating range, sub 2K boost onset, redline is 6000 ish.
I forget why you wanted the turbo[s] out back, if it's astetics this information will not help you.
However, every once in a while you can find a TD04-19G used on fleabay for not much (under $200) if I was close to driving my setup except for a turbo in a home brew rear mount, I would try that one, after porting the waste gate (250 isn't huge, but it's a whole lot bigger than the engine that turbo was intended for).
