340 carb size

I have 2 cars with similar built 340's, b-body with an auto, eddy airgap intake and a 750 vac sec carb and an a-body with a 4-speed, MP M-1 intake and a 650 DP. The 340 with the 650 DP seems to run better. I would like to try a 650 on the other motor and see if there is a diff. The Holley 650 DP seems to be a common carb on 340's and other hot small blocks.