I have an MSD distributor #8582 for my carb'd 302. It came with a cast iron gear that I needed to swap for the steel one. They included some nice instructions on how to do it.
Well, I took it to a reputable shop, they guy is usually really good at this sort of thing. But, when he pressed the gear off, he snapped the other dowl pin in the bushing near the oil seal. No one knew it until it was on the car. (MSD informed me of this) So much for that dizzy, set of wires, and a lot of cleaning. MSD took that one back without a problem, my steel gear was still good, but they sent the gear not installed on a new dizzy (with a cast iron gear).
Part 2 now.. I took the new dizzy back to the same shop to show my machinist the new one, explained the problem with the old, and we took some time doing this swap together. When pressing off the gear again, the same dowel broke. This doesn't take much force either. So he replaced that dowel with a stronger one, got the gear on properly.
It works just fine now. Haven't had a problem with it since.
To sum it up: MSD's customer support is good, my machinist messed up, but made good on it. I'd send yours to MSD, and request that they send you a good one with a steel gear already pressed on!! It may cost a little for shipping, but its well worth it. Don't take a chance. I was lucky that I only lost a set of wires, gaskets, and a lot of time.