I thought that they were the same for FMX and C6, but WCCC shows a large pawl and small pawl version (both out of stock).
I would check with Randy Goodlin in PA ( [email protected] 717-367-7576 )
or Johns Classic Cougar ( John's Classic Cougars ) in MI.
It's possible that a shifter from a 71-73 car with an FMX may work. 1970 was the first year of the FMX and the first year of the locked-in-park shift selector. I recall that the neutral safety switch is different on these also. Maybe you could transfer some of the parts to a good housing.