Could this be a cam timing issue? Is it possible that when he changed out the serp belt that he may have advanced or retarded either or both of the cams? The problem is really close to what I had once in a 76' Torino. I accidentally had the timing advanced by almost 10 degrees and it would die almost every time I tried to open it up, but if I accellerated slowly, it had no problems. Of course, I'm not a mechanic so I could be way off here...
