What is total advance? Mine ran well at 36 degrees full advance, disabled vacuum advance and light spring kit in the distributor. Also, you are running too much carb IMHO for a 340 street car. Stick with a 600-700 cfm carb. A Holley 650 DP is my personal choice. I would look for vacuum leaks around the carb base. Your problem sounds like a lean stumble to me.
Total is initial (at idle) and "however much" mechanical advance is in the distributor. I wouldn't run without vacuum advance on a street car. It'll kill any mileage and also drop off some part throttle response.