I'm thinking not the Fire Fighter kit, since I did find pics of a built original LRE kit, and it appeared to have the correct year door panels (not correct for the truck though, they appeared to be the Custom panels while the LRE was built with the Adventurer trim).
Edit: On the Pumpin' Iron box, you can see the interior panel and it appears to also be the late 70's Custom door panel, so I'm still thinking either the ThunderStruck or Monster Truck kit is when they changed it up.
Edit 2: From some other research, the taillights should be the rectangular "Jeep/Trailer" style, rather than the earlier round style found in the kit. It looks like the round lights were used until 1977, and in 1978 they switched to the rectangular lights. Since the Warlock kit was released in 1977, it makes sense to have the round lights in that kit. Weird they didn't bother to update them for the later kits.