Jet Provost Invertors

After fiddling around in XM354 at brunty and comparing it to the other examples at the field it appears the the invertor and control unit is standard in the hinged nose section (as i fitted yesterday) however although there are positions within the nose assy looking backwards lower left hand side there can be either one or two invertors there and there is no wiring for the earth leads that run up to an earth point in the top left side (painted blue) this is the wire you have to fit internally before installing the unit, is it one or two ???? as well as the afore mentioned one in the hinged section. Is this a T3A mod and what were the main differences between 3 and 3A

Cheers for any help

anyone got a cheap nose wheel or any undercarridge parts non airworthy of course.