Bingo From United States, joined Nov 2006, 339 posts, RR: 0 Reply 1, posted (3 months 1 week 1 day 7 hours ago) and read 2774 times:
Sort of sounds like the
"707-700: A test aircraft used to study the feasibility of using CFM International's CFM56 powerplants on a 707 airframe and possibly retrofitting them to existing aircraft......"
Your inquiry reminded me of this aircraft - built as the only YE-8B (CFM-56 engines) and later delivered to the Royal Saudi AF with serial 1902. It is now designated as an RE-3B.