I agree that the GE38 seems like the most obvious candidate for a "drop-in" replacement engine. As noted the basis engine was the GE27 which was intended for the V-22, so it has the correct basic size, shape, power turbine speed, etc. The biggest changes GE would need to make on the current GE38 engine would be repositioning the engine mounted accessories to match the AE1107C's and modifying the lube oil system for tilting. I understand the GE38's original design allowed for incorporating a lube system capable of tilting, so this mod may not be too difficult.
However, since the basic design of the GE38 is fairly similar to the AE1107C, I can't see what you would do with the GE38 to address the service life and reliability problems that could not be applied to the existing AE1107C.