Yes, a vacuum leak can lead to poor idle. You can use the vacuum gauge and take a reading from a non-ported tap at idle; it should be very steady at maybe 15-19 psi. I'm not sure on the vacuum line condition, but it sounds to me like a good service manual could really help with vacuum line routing. If you're having trouble finding one, maybe try one of the libraries (before our failing city budget closes them, LOL). I've heard folks say that some libraries have them. Maybe try calling them first. Also ask for an emission system book for your model year and see what they have. Personally, I've found Chiltons to be better than Haynes; Haynes often is pretty simplistic and does not go into much detail. If you can get your hands on a CD service manual, that may even be better; the one I have is packed with info that makes advanced troubleshooting/pinpoint testing possible.

On another note, timing must be set properly. This can/will have a dramatic impact on gas mileage and performance. Retarded timing = poor performance = putting your foot into it more = poor mileage. Follow Fords proceedure for starters; tweaking can be done when all of the issues are worked out and it's running properly. For now, go for stock settings.