This site might prove to be a great help, though the M37, basically a
pre-Slant-Six/square-body era Dodge Power Wagon, isn't a particularly
rare or esoteric thing by their standards:
http://www.mvpa.org/mambo/index.php

See also
http://www.dodgepowerwagon.com/main/intro.htm

I'd suggest that you start by reading up on all these things so that
you can learn what to look out for.

The other thing, and I don't mean to sound condescending, is that this
is not even a stripper model of a modern SUV. It is built for serious
work and might well have been used for same. This has a large
influence on its driving qualities and its (lack of) creature comforts,
as does the fact that it is two human generations and several
technology generations old.

Enthusiasts, of course, think that's all part of its charm.

The 230-cube flathead Six needs no such quibbles and excuses. It gave
smooth and torquey service in trucks and luxury cars alike until the
"horsepower wars" of the 50s finally sidelined it.

Anyway, those are the generalities; it then comes down to the
particular vehicle and the pre-auction inspection period. The best
case is that you get a good price on a low-mileage, lightly-used
example of a beast of a machine. The worst case involves 53 years of
Army-type use and Rust Belt winters, together with auction-fever
pricing.

Best of luck,
--Joe