It's a camper, not the space shuttle. There really isn't anything so complex in a 43 year old camper to require a manual.
Like someone else said there probably wasn't a comprehensive manual for the camper. Probably just an information sheet, and then instructions for the individual appliances, which are mostly missing or replaced on yours.
Want weights? Weigh it. Unless you're trying to haul it with a short bed F150 you've probably got plenty of truck.
Be aware that it probably won't fit in a GM made after 1987, a Ford after 1996, or a Dodge after 1993. Those are the old "squarebody" style trucks that were being built in 1979.