74 Duster with 408 Stroker With Dieseling/Idle Issue.

You did not mention the T-slot. Did you take your carb off and have a look at the T-slots? To see if they were rectangular or square? Then warm your engine and adjust the air/fuel. I always ignored this T-slot thing, it does matter.
Sorry to be stupid but I’ve never heard the term t-slot. Please explain.