Vacuum leaks? Do you have a square bore plate under the carb?
What is the initial timing?
There is NO reason that set up should require two footing it to stay running in gear.
If you timed it using the factory 318 mopar settings, throw them away. Set the initial in the 14-18 range and reset the idle/mixture screws.
I'd put a TRUE 2500 converter in it and it should run pretty good. The more gear the better depending on rear tire size. A street car that sees no highway or limited highway use can be geared higher.
