You would be cheaper off rebuilding the 440 for a decent mix of power and mileage.

If he was to swap in a 5.7 and keep the injection, I'm assuming he would be using a factory computer. In that case the sensors and everything is the same as the donor vehicle it came out of. Reliability not an issue in that case because nothing is really aftermarket. So long as the wiring job is done right, you're fine.