The 750 DP is a good carb and will work fine for you. I have used them on stock 383's and Eddy headed 440's. First if the speedo is 10 mph slow that a big factor right there. Heck years ago a tech used to put smaller speedo gears in to let the cust think they got more miles to the gallon. Fix the speedo first. How does it run while driving it. You can fine tune everything but most DP carbs are not that far off on a combo like yours. Ron