[G.R.]

I'm not a mechanic-- but in my other car ,an SPF, I had a 392 and it always seemed to hold about 60psi, hot or cold, hot idle it would drop if I had had been driving it for awhile and was in heavy stop and go traffic to around 45-50, may have been the gauge because I really don't know.
As for your miss I suspect that it could be due to the MSD--I read the manual and vaguely remember it cautioning about disconnecting it before doing any type of electrical work or welding. I do know a welder in proximty to "live" electronics can mess them up---can you borrow a MSD and temporarily hook it up to see if that is indeed the problem? I maybe way out of the ball park here.