You're going to have a problem, Zac. The old Hasegawa kit doesn't reflect the line changes for the Spey installation and the nozzles are undersized for a proper Spey (note that Revell did the same thing in 1/48 around the same time, some 40 years ago, with the same result). Using aftermarket nozzles, intended for the Fujimi kit, will definitely show the difference and be a bother to fit properly. I think I can find my copy of this kit and will make the nozzles available if someone wishes to make you cloned copies; I want to keep the nozzles because they can be used as the base for PW1120 nozzles, with 1/100 F-15 nozzle flaps, for various upgrades.
HTH,
Evan