The annual kit/promo body was used, with the stock bumpers and windshield wipers being left alone. That was true for all of the MPC pro stock kits. They liked to get two kits per year off of the annual kit bodies, the same was often done with the funny cars which was why there were Dodge Coronet and '70-'71 Mercury Cyclone funny cars which nobody ever ran in the real world. The Mustang II (and Vega) rear wheel openings got modified back and forth, by the time the last annual kits came out the quarter panels on both were really lumpy. The engine being too far forward again goes to MPC having to change the kit back to next years' annual kit. Even though they weren't doing Mustang II promos after '75, the annual kit was one of their better sellers each year so it kept coming back.
--Mark