My guess is the timing chain. If the former owner replaced it with a double roller, the block should have been notched to receive the chain. What I mean to say is this. The block needs a little messaging just above the cam area. This then allows the cam and chain to sit in proper alignment. Add to this, it should have a timing chain button installed. This button rests against the timing chain cover and ensures that the cam does not walk forward.

It is an easy fix.

If the above is not the problem, and if it is an automatic, possibly the torque converter wasn’t installed properly into the tranny pump and is pushing the crank forward. Ouch!

BTW, whatever happened to streets? It seems to be safe to post again.