My 2¢ Perhaps it should count if the jet engine was intended to provide all or part of the power so that the aircraft could fly, but not if the jet was merely carried aloft by the aircraft so that the jet could be tested. The "not intended for production" clause might rule out quite a few of them, and I don't think that is what we want here.There are two P-51Ds that would *technically* qualify, though they were only test beds.
One of the tests, had a P-51D fitted with two XRJ-30 ramjets (one in each wingtip).
The other P-51D was fitted with two PJ31-1 Pulsejet engines, one under each wing.
This is just for fun, by the way - they shouldn't be on the list because they were just test aircraft and not intended for production.