For an XR4Ti, I'd think you'd want an F150 3.5, due to it being mounted the correct way for your RWD need. Not sure what trans you could mate up with it for RWD duty. I would imagine the bellhousing pattern would be the same as any 2.5/3.0/3.5 Duratec engine (totally guessing here, but based off of Ford engine 'families)...