Back when the Concorde was in development, a guy I used to work with was in West Africa with G-AXDN doing hot weather trials. The aircraft had an engine issue and an engine had to be changed.
This aircraft had production standard engines. No spare was available so an earlier variant was installed and some of the accessories were left off and the air bleeds blanked, as they would not fit this installation.
The aircraft was ferried back to Fairford with 4 engines but only 3 sets of systems.