What stall converter?

Listen to Crackedback.... Best knowledge ever.

A simple way to determine what converter is needed, have your stall just about 200 rpm above the beginning powerband of the cam. This is a rough idea but gets you in the ballpark.

If your 508 cam was stalling going into gear with the stall converter you said, once again Crackedback said it. Sounds like initial timing. That cam needs about 20-22* initial timing to run good That is where custom advance bushings for MSD distributors come into play so you don't go more than about 34-35* total.