Been out to Carlisle and just got back, while there I picked up a book that I had never seen before for 77 Dodge trucks. It is the 1977 Dodge Truck Sales Manual. In it it breaks down standard equipment, available packages, whats new for 1977 and additional factory installed options. It covers all trucks, Ramchargers, Sportsman wagons, Tradesman Vans, d500,600 & 700 trucks, Motorhome chassis pretty well all aspects of the truck line for that year. There were some options that I had no idea were available and were a first for that year, but my point to this is in the additional factory installed options for d100,d200,d300,w100,w200,w300 and w400 it lists and I quote "HL4 In-cab 24 gal. cap. mtd. behind seat on conv. or crew-cab sweptline pick-up models N.A. w/hinge-back bench seat" so it was available but the seat would have not folded forward, as in the bucket seat "buddy seat" package like in my truck or a fixed bench seat that did not fold forward. So I think there is the answer as far as 77 is concerned.