OMG we're giving our ages away now arent't we? I'm with Chris on this - the good old days of Pinto - get a Corsair bellhousing and stick an Essex V6 on the front - then watch your fuel tank implode as it's sucked empty!!
But more seriously, some of the Japanese machinery might make a better switch. My Mitsubishi 2.5 24valve V6 developed 161 bhp and drove like a dream. The Explorer gets a pitiful 200bhp from its 4 litres so what's it doign with the rest?
The Mitsi engine is the same as used in the Shoguns and their other off-roaders - even the 3L is the same motor but Chris is right - there's a lot of computer to transplant with anything of that nature unless you fancy going back to carburettors etc. I've seem some nice work done with Toyota hardware too. I know a guy who built a 24V 3L Supra motor onto a Land Cruiser box and running gear. That was manly enough.
A 200TDI? Do you not have enough pain in your life? I know they drove well while they worked but bloody hell, the dealers were breeding the damn things at their height - all parked round the back, all seized on one cylinder. Nuff said!