[BILL WILLIAMSON]

Have you checked the compression? Just off hand, "might" be a burned valve, or a valve adjusted to tight to close completely?? Does any cylinder have a complete miss? "Might" be a slightly sticking valve. A compression or a leak down test would be the first test to rule out compression problems.
Check it in the dark, "might" be the conductor going to #4 cylinder, in the distributor body, arcing out the top of the body, to #3 plug strap, I'm not sure if that would give you jumping guage readin, or not. If it's the arcing problem, it'll cause a miss, BUT it's usually erratic, NOT a constant miss. Just throwing out some possibilities,---As it's been a looong, tiring day & my "brain"?? is TIRED!!---Bill W.