What are you referring to??? All 1985/86 Mustangs had the 4-eye front end, none were "new headlights" or came w/ the Aero (87-93) nose (if this is what you are referring to as far as new headlights... 1985 & 1986 is also the only years the Mustang had the same front bumper cover (ie: no slats or actual grille in the center section), but still had the 4-headlight system as the 79-84's. Are you referring to the "new" headlights as being different from 1979-1984??
Unless you have a rare prototype or are saying your 1987 Mustang is an early build (hence 86.5) there's no such thing as an 86.5 year Mustang with the old dash and new front end. The only other way this would exist is someone put an aero front end on your 86 Mustang...
Not trying to bust balls or put down your vehicle, however, you need to clear up your statements as to what you actually have in your posession.
To some, "new headlights" refers to the upgraded 1987-93 front bumper cover w/ the plastic aerodynamic headlights.
back ttt - good luck w/ your sale.
Post up the VIN and pics, please.