1974 F100 ignition timing

I own a 1974 Ford f100 3spd auto. 302 engine.

In December the timing chain broke, snapped my camshaft, toasted the engine. Had another 302 put in, and went to pick it up today after it was finished Monday. Had been sitting in below zero weather since Monday morning. Finally got her started and down the road. Wouldn’t even hit 40, pinged like crazy. Found out the timing was retarded. What can cause this? Other than a loose distributor bolt? I want to avoid this in the future. My mechanic kept it in his shop overnight and is planning to cold starting tomorrow morning to make sure everything is running fine he timed it out correctly earlier tonight drove around for a while make sure everything was driving fine and it was after it was timed . I just want to know if there’s anything that can cause ignition timing to retard itself. And how I can avoid this.