Well done f1fan.
Bob Tullius called it the Jaguar XJR-8 and everyone else the Magnum 44.
It was built into a working car but cancellation of the contract prevented further development.
All-
This car was called by several names. Tullius wanted "XJR-8" though given the number sequencing at the time it probably should have been the XJR-9. It earned the "44 Magnum" and "Mag-Jag" sobriquets from the crew due to its experimental magnesium block Jaguar engine. It is indeed a development of the XJR-7 and was constructed from XJR-7 chassis #005. It was never raced, or fully developed in the era. Group 44 tried to market this as a customer GTP car, ala Porsche's 962, so it could be fitted with mounts for Chevrolet or Ford V-8 engines, but there was no interest. As it is currently run in vintage races it uses a standard aluminum Group 44 Jaguar engine, as the magnesium engine deteriorated badly over the years.
-Rick