I've bought repair manuals for most of the vehicles I've owned over the years. Most of these have been from Haynes because they are easier to find. Haynes repair manuals tend to be generic for a whole series, with tables of information to cover differences year to year. For example, the Haynes for your van now covers 1971 through 2003 model years (32 years building essentially the same van with running changes in bodywork and mechanical options). Similarly, the one for my Ford van is 1992 through 2014. It is almost the same van as the one covered by the Haynes for 1969 through 1991, got a new front end and new engines in '92. Dodge didn't get new engines.
I've bought Chilton manuals for a few import cars in the 60s and 70s, liked them better because they tended to be more year specific, and more detailed but that also made them more expensive and harder to find, because the year you're looking for can be sold out and out of print. For example, I can no longer buy the Chilton manual for my 1965 Renault R-8, nor for the '68 BMW or '71 Audi, but I could get them when the cars were more current.
My dad's repair shop usually bought the Chilton manuals if they needed information, before springing for factory manuals (or caging a look at a dealer's copy). Chilton manual for your van covers 1968-88 and include information about the cutaways and the small motorhome bare chassis.
Haynes manual covers a lot more work than I can do myself, and growing up around an auto repair shop, I've been doing or watching the work since about age eight or nine. Early imports particularly needed a lot of TLC.
Be aware that both manual series assume basic mechanical skills, some experience, and knowledge of the vocabulary. Haynes manuals have some basic how-to and safety information in each one, but not like having had an auto shop course. Which would not be a bad idea, if your local tech school has a course for hobbyists and owners.