One other item, most mechanics these days have never seen a Pontiac OHC6 much less worked on one. I say this because with the cam belt, the engines sound a little different. You tend to hear the valve tappet sounds a little more pronounced with respect to the overall engine noise. So the guy probably had good intentions, it just sounded a little strange to him.

If it looked like a gnarled mess after he reopened the engine up, then he probably screwed up. If on the other hand the hydraulic lash gave out, its probably no ones fault. Its simply one of the joys of owning a 40+ year old car.