Still has a stumble/hesitiation

Just for sh*ts and giggles, I'd try a smaller carb, say ,600 Holley or 625 AFB. I think 750 is just too much carb for a 340, unless you've got a huge cam,pistons, convertor and gear to go with. I see some guys w/ 408's running 625/670 carbs...(shrug).

Just my thoughts....maybe worth what you're paying for 'em.....