Backfiring is gone. My best performing timing is about 16 at idle, 30 at idle with canister connected to constant vacuum port on the carb, and about 50 total all in. (My timing tape only goes from 15 to 40).

Vacuum is about 18" at idle. 180 thermostat. CH14YC plugs.

If that seems OK to you, what would be your first step with the Edelbrock 1413 800 cfm carb, keeping in mind the stock cam. It appears to have silver 8" vacuum step-up springs in it, not orange (5" vacuum) springs.