Think of it as a bigger version of a SIII Landrover, simple chassis, hydraulic brakes, cart spings, live axles, 4 speed gearbox, 2 speed remote transfer box rather than bolted to the gearbox, 12v electrics.
The cabs rot badly, the pikeys steal the gearboxes, you bash your left elbow on a cab seam when changing from 1st to 2nd. The chassis is extremely flexible by design to give a good cross country performance, so beware of fitting a rigid body as it will have a hard time. The army ones have a steel body, the AFS ones have a slightly longer wooden body. Access to the engine is good as the engine cover opens in to the cab, while a clutch change can be done in half an hour including tea breaks.
Theoretically there should be no problem with mechanical spares as the AFS kept a huge amount which were sold off after the GGs were released.