I'm pretty sure the magnums that year should have 45-52psi in the rail before startup, 12-14 I'm surprised it's starting at all. Try getting a can of carb cleaner and keep it running on that, it will at least narrow down between fuel and spark. Just to make sure, your rail shouldn't have a regulator on it being a 94, but 92-93 does (I think?). Just picturing your setup, my 68 fury is 94 obd1 5.2, so probably very similar.