Since when does spark plugs cause low fuel pressure? Thats still an issue he has, and needs to be resolved. Though I wouldn't have used already used spark plugs. There too cheap to be doing that. Get some Tr6 plugs and gap at .035.
Back to the fuel pressure. Your using a handheld gauge right? Because I just had an issue with my autometer gauge messing with me and reading low, so I went and finaly bought a handheld universail kit, and hooked it up to find my fuel pressure was fine right were it should be. Wild shot, but maybe try another gauge if you can. Buy one and return it if you have to. Make sure it will fit Ford small schrader valve, and is not for carbs. Most efi kits are fine. I picked mine up on sale for $40, listed at $55. Sorry to make you run around, but you do need to get that figured out, it may or may not be the cause of the misfire. It at least has to be ruled out.
