Early 273 intake problems

Sorry I’ve been absent. Work and family stuff. Thank you all the responses so far.
This is where I’m at today (with y’alls help)...

I feel that the Offy is for a later model and I definitely have 315’s heads (273). I think I’m going to sell the Offy. It’s soo nice, I don’t want to be the one to mod it. Plus everyone is saying that the quadajet is a pain to tune. I’m waiting for a phone call to go get a performer intake. Yes I know I have to mod it.

Now as for the carb problem. I have had 3 different carter bbd’s on it. They run fine for a short time and then go to hell. Won’t hold an idle once hot is the most common problem. The last one I had the idle mixture screws out 3 1/2-4 turns just to get it idle cold. Forget about it idling once hot. Yes I checked for vaccum leaks. I’m done with 50+yr old carbs. I’m buying a brand new carb today. But which one. I’m debating on putting a small cam in it. I plan to drive the hell out of once it runs correctly. I was thinking a 500cfm Edelbrock AVS 2. Is that enough cfm with a small cam? The problem is the AVS 2 jumps to 650cfm which I feel is too much. I’m not sure I can jet it down enough to run correctly. Thoughts?

The specs are:
273 2bbl engine with 2 1/2in dual exhaust
4 spd trans
2:94 rear end
25.4 tall rear tire