[COACH MIKE]

Gentlemen:
I have just added a MSD 6AL ignition box to my ignition set up (408 stroker). I had a ford (heavy duty) ignition box with a MSD Blaster 2 coil and MSD billet distributor. Once I got the MSD 6AL hooked up properly the car started but ran very rough and I could hardly get any rpm's out of it. It sounded as if the timing was off drastically. The timing had been just right prior to the instillation of the MSD box (18 degrees initial and a total advance of 36 degrees at 2800 rpm).
I set the idle up enough to get the engine to at least idle at 900 rpm. When I checked the timing it was retarded considerably. I than advanced the timing to the aformentioned specs and the engine runs fine. Has anyone else experienced this phenomenon and if so can you explain why and if something is wrong?
Your experienced suggestions are much appreciated.