I'd personally look into one of the straight 6 XJs. Turning circle is a bit big. h:

There's also the famed Chevy small-block conversion route...that'd be fun..:driving:

Oh, and AVOID THE JAGUAR SOVERIGN AT ALL COST. It is an absolute basketcase. The entire multiplexed wiring system is a disaster. If you are given one, then only consider it as a candidate for a SBC conversion, done in concert with a complete re-wiring of the vehicle, aftermarket fuel management, the works.