I have a 1971 Pontiac Ventura. It was originally a 6 cyl car. When I bought it a few years ago it had a tired 305 in it. My son and I swapped it out with a 496 stroker. It makes 475 hp. We initially put in a MSD 6AL ignition box. One mechanic said it was shot? so he took it out saying I don't really need an ignition box that big anyway. He put in a cheap $50 distributor from one of those discount distributors and it has never run right ever since. It will fire and run and rev like normal, but as soon as it gets under any load she starts missing and sputtering. Oh yah, it is still the original wiring. Any help would be appreciated.