I replaced a water pump on a 1966 Dodge once. It was a six and it was very difficult. Later I learned that the entire engine cover was usually removed and this would have made changing the water pump easy.

But removing the engine cover was a big job as well.

Vans of the 60's had radiators that would cool the engines. There was no room for a larger radiator and A/C was unheard of in a work van. For this reason most of the vans then that had A/C had aftermarket units with the condenser mounted on the roof. I am sure advances have been made to make sure it all fits in like it should, but the ac vents still need to be mounted on the ceiling if it is possible.

They do handle better than you might think since a lot of them could be called mid-engined. But with the engine mounted between the front seats it can get rather hot on a long trip.

Gas fired heaters were also common. If you wish to add or replace one of these they are still made by WEBASTO and they are much improved from the ones that were made back then.

I am not trying to discourage you. Any car 50 years old is not going to be up to today's standards.

At one time the 'forward control' vans were thought to be the hot item with collectors but I think this has cooled off a bit.