i don't think there are any forums that specialize in the bigger dodges. this forum works pretty well, though, especially thanks to bob.
mine's probably about what you want, as far as a place to start. it isn't pretty, the sheetmetal has been patched, it has a lot of bumps. the frame is almost perfect, though. i got lucky. this truck was highly optioned. triple overriders, two sun visors, 2-speed, fresh-air/heater, extra frame side-sill.
if'n i were looking, i'd absolutely get one with the 2-speed rear end (which mine has). makes it much more road-friendly. i can cruise around 45 to 50 comfortably, still puts it under 3200 rpm. the later years in the p-h series have a bigger motor than my 237, but it works fine. the dump body is usefull, and as mike (fowler) points out, these trucks will carry WAY more, comfortably, than they are rated for.
midwest is a great place to find one that has been in grain service on a farm forever. mine came from michigan. craigslist is a good place to look, too, using expanded search options.