We- wife, me and one or two biggish dogs(greyhounds) travel in out 1998 Suburban.
Two adult humans+ 1 or two dogs sleep in the back at rest stops on a double mattress-a double mattress - floppy futon mattress fits just fine in the back of a Suburban with the second row flat and 3rd removed.
It is almost like sleeping on the bed at home- except we don't sleep with the dog on the bed at home.
Arty- the dog- would be up for sleeping in the bed at home, but I don't need a bad breath dog hogging the bed at home!!
My point-I have eyeballed vans- they are pretty tempting for the comfort, but the Suburban is pretty comfortable on long trips,and in general it is easier to find a good Suburban than a good van.
Also- 1996-1998 Suburbans are pretty cheap around here-maybe $2500-$3500 max!!
You will do alright either way- but the Suburbans are pretty good travel vehicles-get good mpg also- 19-20 mpg at 65 mph-
Dogs love the Suburban- sure they would love the van also.
I replaced the 350 in my Hi top conversion van with a 383 stroker. It was not that bad! You do have to remove the front radiator support and grill assy. Remove the A/C condenser, power steering bracket and pump, a/c compressor, complete intake assembly!!!! Remove the front bumber and you are close! Next remove the exhaust manifold bolts, power wire from computer area to batt pos. remove the torque converter cover, remove the 3 torque converter bolts, drop the starter, Oh yea the dog house should already be off! remove the 6 bolts holding the trans to the engine and you will need to remove the complete motor mount assy 3 bolts each, now the tricky part... you need to remove as much slack as you can from your engine hoist ! you need to remove whatever hook is on the hoist arm and replace it with the shortest double sided eyebolt (habor freight $2) that has a removable pin. Then you need to stretch a chain across the front to the back of the engine as low and as tight as you can get it!!!! Even with the intake off there is not much room to lift the engine with the hoist, The hoist comes very close to the cowl/firewall and really limits how much you can lift it! I got my engine supported just enough to wiggle it out enough to clear the firewall and lift it the rest of the way to clear the lower radiator support. Sounds like a lot but not that bad to do! I some cases it was nice to be able to reach stuff from inside the van because the dog house is off!