There is much similar between them from '72 all the way to '03 when they quit (unfortunately) making the B van. there are breaks from 72-78, 79-93, and 94-up as far as interchangeability. Suspension went 72-78, 79-97, and 98-up with some parts overlapping those years. They changed to a big bolt pattern (small was 5 on 4-1/2, big was 5 on 5-1/2) between 84-85. the 78 model mechanically was the same as the 72-77s but seemed to be a phase in to the 79 up as they changed the taillights to the newer style but kept the old front clip 1 more year. the "cheapie" models from 79-85 could be had with single round headlites, the "better" models had 4 rectangular ones, 86-93 had 2 square ones. From a 150/1500 "1/2 ton" to the 200/250/2500 "3/4 ton" there was little difference, like heavier springs, but both 1/2 and 3/4 were 5 lug wheels. You have to get into a 1 ton to get 8 luggers; heavier rear end, (these weren't duallies except the Kary Vans...box trucks, or motor homes) bigger brakes, suspension pieces and such. Most 1/2 and 3/4 tonners I've seen had 8-1/4 rears, a few 8-3/4 in the early ones a few 9-1/4s here and there, too.
Til 78 all autos 727 trannys, 79 up could be either 904 variant (998-999) or 727. Also could be had with a big block til 78 as well. Slant 6s went away after '87. Could also have had a 3-on-the-tree manual or an 833 OD.
Very easy to work on, (tune up wise, etc) engine covers were easier to pull than Fords and Chevys, water pumps,alternators, belts etc a little tougher than say a pickup to access but still not bad. I know I'd buy another one in a minute if I was in the market for another vehicle....... My last one an 87, B 250 long wheelbase (but not a Maxi), 318 2 bbl, A 999 trans, 2.94 rear, was dead solid reliable and my boss at my old job could never understand how my "big tank" out MPG'd his wrong wheel drive fuel injected 3.3 Voyager! And it towed anything I ever asked it to.
OOPS!!! I didnt mean for this to be a new topic, but "fat fingered" it when I went to reply to the original question.

Thanks for all the info on the vans. I'm researching between Phord and Dodge trying to see what will best suit my needs. Is there any major problem areas I need to be aware of, common failures, engineering problems, impossible things to fix, etc?

How are these things on gravel roads, snow/ice, and what kind of trailer towing ability do they have?

Thanks

on gravel/ice, just drive decent and keep good tires on and youll be fine, a little weight in back dont hurt. On the fords, stay older than 92, when they had kingpins more reliable than the 92-up ball joints, made much more $$$$ as an alignment guy on these than anything else except maybe Exploders and S 10 Blazers. (the aftermarket greasable Moogs helped some though.) Still did multiple replacements of them on the 92-up models... the Dodges were good for upper BJs around 125K under average conditions, and occasional idler arms... these had 2 per van.
I have never owned anything but Dodge products since Ive been able to drive (OK,OK, so I have 2 Jeeps... but theyre Mopar too, since Mopar swallowed them up... right?) I always hated working on Fords they did everything bass ackwards especially towards the end of carbs and into EFI. One consideration from a friend of mine that subcontracts for a delivery co; He had his heart set on a Dodge, but for some reason he had to unfortunately buy a Ford van because I guess they have bigger cargo door openings and the co that he works for specified a min size and the Dodge was close but not quite. Aside from that I wouldnt hesitate to buy another Dodge van!

I have retired my 350 dodge to the side yard. It was a great van. easy to repair. It didn't like high winds but i never felt unsafe. The 318 seemed powerfull even though well worn out, with it's automatic oil change. The rear spring shackles don't mount to the frame, but to the sheet metal floor. i used a length of steel beam across the back of the body with the rear shackles mounted to that after they pulled through the back floor.

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"It ain't a truck if you can't hose out the cab."