First things first...Welcome to FABO and congrats on the Valiant!! All of the mechanical elements are the same, brakes, rearend, trans and such. The grille and trim will be different from year to year, but would still fit as a complete swap. The door panels will probably be different as the 4 door skins will be shorter because 2 and 4 door doors are different. The windshields will probably also be different and the rear window also, as the 4 door cars windshield are usually set steeper than the sedans. Obviously the front seat of the 4 door will not have the tilt back that is needed to get in the back seat of the 2 door. The dash will probably be different cosmetically, but is still a direct swap between years.
My advise???... Get the 4 door also, as it will be a wealth of items, big and small, which will make your restoration much smoother. Also, it will serve as a visual textbook of where and how things go together as you dis-assemble the 2 door for restoration. You just never know what you're gonna need, and it will be much nicer to just go out to the 4 door and have the parts rather than searching here, there and probably everywhere looking for needed items. Welcome again, and welcome to the FABO ranks!!! Geof