I have a Duraspark on my race motor with the MSD 6AL. The vacuum has been removed and the plate locked down. Much cheaper than something else, its a rebuilt unit from O'Reilly's. I took the cast gear off and put on a bronze gear due to the solid roller cam (289). It's been in there since '94, had about 200 passes on it and finallybroke the roll pin. It now has a cut off nail with the ends swedged in its place (race track fix).
I've been runnnign one in my 66 coupe for about ten years now. In fact, I recently pulled it in favor of an MSD unit and ended up putting the Duraspark in my 69 Falcon wagon. The only problem I had was burning out the original magnetic pickup a year after it first went in.
I ran the Duraspark on my 460 and my 351. The only problem I had was as sheared roll pin, but that was my own fault. Never had any other problems though.