65 stanggang, proeagles makes very good suggestions. I believe anything from 600-750 would be very workable. Good luck with your project.

 

And you just reminded me! Those nasty power valves were vacuum controlled, had a small rubber diaphragm in them. Low vacuum (high engine demand) caused the valve to open against spring pressure, to richen the soup. I once had one with a crack in the diaphragm. It burned fuel like crazy! imp

 

IMP, as usual, you hit the nail on the head. After 60 years of building high performance engines, I swear, one of the most misunderstood items is the Holley power valve. Knowing the engine's "Manifold Vacuum" is key to choosing the "optimum" power valve. I always take your inputs very seriously.

 

65stanggang, your head must be spinning after all of the suggestions that have been presented. My curiosity has gotten the best of me. Were you able to correct the issue by working on the 780, or did you decide to go with a different carb? The 351 is a very cost effective block for the cubic inches and potential power output. Any information/input I can receive will help me when deciding on different 351 packages. Of course there will be different "combo" due to the many different applications that people are applying their priorities to. Any info would be greatly appreciated.