i purchased a Road Demon and had troubles trying to tune it on the bottom end. I called Barry Grant's tech line and the only help I got was you should have purchased a 650 Speed Demon. I did a little digging and found that the only difference between the 725 Road Demon and the 650 Speed Demon is the main body and main jet sizes. I again called Barry Grant to see if I could purchase a main body and was told no they don't sell them as replacement parts.
IMHO, I would stay with holley, there are 100's of folks that specialize in them and you can get any part you need either from Holley or the aftermarket.