A full size van with 8 lug wheels could wither be a 3/4 or 1 ton, it will have a full frame just like a pickup only with the van steering setup. The astro vans were kind of uni body, they have a subframe under the front and back, not sure what connects them together. my buddy made a jacked up 4x4 out of his but i did not spend much time looking at it, he just told me that he made new subframes and bolted them in place of the originals.
I think you are getting there, it helps to spend the time up front to compare your options and check each one out in person.


1937 GMC T16 468 BBC th350, 4.10
1941 Dodge COE 5.9 cummins, 9 speed roadranger
1947 Diamond T COE, hercules and 4 spd, all original
1955 Chevy LCF 9.0L IH diesel AT545
1962 Corvair (Elsie)
1967 Jeepster Commando
1968 K10
1970 Chevy C50 box truck