i've often wondered how hard this would be to do with a turbo diesel manifold. i'm sure you could kill a high mileage engine quite quickly. also if it was that easy you'd have probably seen alot more of those type of conversions going around.
not saying it couldn't be done, i'd like to know myself, but it may just be a cost factor, like topher said, its probably easier and cheaper to do a transplant. let us know if you have a crack at it though....