Doesn't work like that. They want to use a J28D engine modified for super sonic flight. That engine was designed to power MD80's.
JT8D [0] is based on the J52 engine that powered the A-4 Skyhawk, and a related design is the RM8 [1] that powered the M2.0+ SAAB Viggen.[2]
[0] https://en.wikipedia.org/wiki/Pratt_%26_Whitney_JT8D