No experience with Ford but +1 on David's suggestions. In my own endless frustrations I have discovered valves too tight will backfire, lean conditions will backfire, and misadjusted timing will backfire. I have found problems in the Holley accelerator pump, the idle transition, base versus total timing and the curve, the curve ramp, secondary springs not coming on right among the villains. One tremendous issue I had was believing that my distributor was installed correctly when it was one notch out. Also had problems getting it 180 degrees out.. If it isn't the firing order bring her to TDC on number one, make sure the timing mark matches TDC on the arrow. This is the fun you signed up for. Also read your plugs once you've run it a few minutes