doesn't the A/F gauge use the o2 sensor? and the EGT uses a probe that needs to be drilled & tapped? Anyways, I think Matt? (Chipmunk) hooked up a A/F gauge in his GT. Maybe you can check with him about the install. Good Luck!
Kevin & Donna's Elec Blue GT
Pictures of our PT GT
http://www.dreamcruisers.org/index/Page_1x.html