Cignificant,
So you're saying that a Crane ignition box is compatible and works well with a Merc Thunderbolt distributor whether the engine is blown or N/A---right? Thanks

I have the msd billet dist, and 6 box in my 400hp sbc p/u and my 73 vette w/ about 435hp for well over 3 yrs now with no problems. I also had it in my scarab that was in the boat when I got it and was working perfect when I sold it 3 yrs. later. Just my .02

KAAMA - yes. You do have to "phase" the Thunderbolts by drilling holes in the silver-spinning-thingy (sorry, I don't know the technical name of it) under the cap. The instructions that come with the Crane ignition boxes tell you what to do. The nice thing about the Cranes is that you can set RPM limit and advance curves with dials on the box. No plug in "modules" or boxes.