I did some checking and I have several thoughts for you.
1st, taking a step back - a motor (and tranny) with 100K on it already is a cause for concern. That's pretty high mileage for a motor you just want to drop in and not worry about. How was it treated during its lifetime? Were the fluids changed often, etc?
2) 403's are a lot of heavy cast iron for the amount of power they put out stock. They can be hot rodded, but not very easily.
3) I could not find a single vendor that had conversion brackets to put these in an FGF. And the vendors that had the REGULAR brackets to put a 403 into a 2nd Gen F-body said those brackets were discontinued.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
