Dealer Special Order (DSO) kits were available to convert a 'regular' Mustang hatchback to a look-alike M81. This is probably one of them.
Being a 1982 model it is not a (1980) M81. It is very unlikely it is an Enduro GT. Two of the three Enduro GTs are accounted for.
Check this thread on FEP: https://vb.foureyedpride.com/showthread.php?193948-1982-GT-Enduro-DSO
I suspected something like that but could not find info on it anywhere. Nice find
Open the following link in Chrome to see the page format correctly:
http://vb.foureyedpride.com/showthread.php?193948-1982-GT-Enduro-DSO