I didn't see a response about what your timing is set at, so just an FYI, Eddy headed combo's like about 34°. I would make CERTIN that your timing is correct before you get too far.
For what its worth, I can literally slow my car down by 4 tenths of a second by removing 7 degrees of timing...which is why I say check your timing.
The tune on the carb is the other thing that could easily slow you down. Check your plugs, go to a test and tune night and get that carb dialed in (jet up until the MPH falls off, then back it up 1 step and you're golden). I can explain this in detail if needed (just ask).