Avs2 650 tuning on a 340

The starter not acting good when it's hot could be a hot starter not the timing so much. Usually the first sign of the starter not working well... I too have somewhat a similar setup with maybe just a tick more cam. I am running dual Holly Street demons which are basically across between the Edelbrock and a thermal quad. Also metering rods step up Springs same kind of gamma-rama..
I'm sure in the Edelbrock instructions it talks about long duration cams? And the possible necessity of a weaker step up spring. When you say it's bouncing maybe that's what it wants to do.
The real name of the game here is just patience. Writing down what you've tried and writing down the different combinations. Test and try again always with a warmed up car. You can imagine with two carburetors that were never supposed to be put in a dual quad situation I had to do this dozens of times before it got right..
He might try taking one of those Blue Springs out and putting a light silver spring in. Make the timing come just a little quicker.. beyond moving the arm for the pump squirter you can purchase larger squirters to put in there as well and there's a different pump you can put in as well.. all cheap stuff to buy to give a try. When I read your first post I was pumped shot as well but I think you're getting real close. Also I like putting a new set of plugs in and driving it for a day or two and seeing what they look like. A lot of times the O2 sensor isn't everything but plugs never lie.
I seem to live with high 13 low 14 at idle and mid to low 13s at Cruise and about a 12-3 at wide open throttle sometimes a little lower..