Yeah, a 780 is too much carb here.

That's the problem with taking advice from racers, they have no concept of how that will work effectively on the street, poorly is usually the answer.

Can that 780 be made to work, well it's "working" right now.

But can it be made to work better? Yes and I suspect your friend tuned it for WOT and nothing else because it sure isn't acting like it is tuned for anything else.

It is the best choice for what you are doing? Nope. A 600 or 650 would have been a better choice, tuning it for all modes of operation would be a better choice as well. Not quick or simple though,

Someone suggested a Edelbrock AS of similar size to the stock AVS, thing about that choice is you could start with the same jetting, rods, etc as the stock carb and have been way closer to the proper tune from the start,