I don't have a technical answer, but I can tell you that an MSD "ready to run" distributor ran in my vehicle for 2, and 11 minutes total, and dealing with MSD was like dealing with an insane person. I sent it back after each failure. First they acknowledged the problem, then told me they couldn't fix it because they didn't have any parts, then they said they couldn't re-use the existing distributor (with new parts) because it had been drilled too many times (once by them, once to put on the new and correct gear), then they returned it saying there was nothing wrong with it, then it ran for 11 minutes. They then claimed they couldn't replace it because MSD didn't have any MSD distributors.
My point is that with a Duraspark you won't have any factory support, but you won't be paying for it or expecting it.