This is an interesting problem, and i’m curious as to what’s the problem. Probably not an issue with yours, since you mention you don’t feel it nose over, but did you change the fuel tank or setup? Is the tank system properly vented? I had this problem on my 73 b body, and had to repair the tank venting. But, i felt some nosing over when i hit 2nd gear shift. If you jet up and still no richening of plugs, as you stated, there is fuel system problem. Venting is one area to double check. Good luck.