Rob Griffiths' "Chieftain" has a couple of pages on the Jagdcheiftain. The jist of it is as follows:
Jagdchieftain, or rather the Concepts Test Rig (CTR) was a 1972 joint project between UK and West Germany. This had a semi-fixed weapon in a hull superstructure on a Chieftain chassis. Modifications were made to the suspension, gearbox and steering system to allow the vehicle to be slewed for fine tuning when laying the 120mm weapon. A dummy gun was fitted to the vehicle that has been pictured previously. It was designed to used either the L60 or MTU pwerpacks, the MTU being in use on the Leopard.
The glacis was to be heavily armoured against all current and future AT weapons and this was intended to be Chobham armour. This was not fitted to the prototype, but was simulated by the addition of 5 tons of lead plate covered in sheet steel.
Three-man crew (commander, driver and loader) with the vehilce being capable of driven backwards, as has been mentioned in previous posts. Driver and commander were to be able to drive the vehicle, while the loader had a rear vison block to allow him to drive it backwards.
While the vehicle performed well as a test vehicle for the drive train, the gun laying trials showed it to be inferior to a turret for speed in engaging targets, so it was cancelled.
Rob mentions that the Jagdchieftain was based on the FV.4211 "Aluminium Chieftain", but doesn't elaborate on that apart from the fact that it was kept in storage to monitor the aluminium welds. Perhaps some-one in the know could elaborate further on the Aluminium Chieftain.
KB