[racer]

imho, adding 50-70hp to a car should imply more than just an engine upgrade, but also brakes, suspension and, given the narrow body of the '76, rear flares. Yes, I know its possible to enjoy a conversion car without all that other stuff, but to me, its part of the larger "done right" conversion.

That said, I'd be inclined to simply remove/rebuild/repair the existing 2.7L motor. Plus, assuming its a "number matching" car to begin with, any value will only increase with time keeping it as such.