Wrong carburetor?

Hi guys, I have a problem with my cars: the penultimate weekend I drove about 30km without any problems. On the way back, just before I was home, the engine went off when I had to turn off before. Engine on, gear in and on. At the last 50m the engine went off again. He left without any problems, but as soon as I put in a gear he went out again after about 1 second… nothing went except the neighbor who pushed me home — After about 2 hours of cooling you could drive again. This week I had a friend of the carburetor set and he slightly raised the idle speed…..but the engine went off 2 times when running warm in the stand. On a test drive he went out once when we were in front of a crossroad. But then he drove again to the vehicle: it is a 64er Impala with 327er engine (300Ps) and a noblebrock 1407 (750cfm) carburetor on (probably) original suck-in pi nne and there’s nothing to see from an adapter plate! I’ve already spent a few hours in Inet and read a lot about the topic and guess that it’s the carburettor because it’s probably more than too big for this engine?! According to the formula for the carburettor calculation, I’m guessing 402 Cfm as a result! What do I look like when I swap the carburettor through a 500 CFM? Does that fit, or is it too big? Before I throw out my money to the window, and the error v I hope you can help me! mfg Stefan