They are an interesting piece of work. The Clark Cortez is the older, very short one. It morphed into the Kent/Alco Cortez (I had one) which was still short but more of a luxury motorhome. Biggest difference was the engine layout--a 225 ci slant six Chrysler in the early Clarks and the complicated, thirsty GM 455 FWD setup from the Olds Toronado for the Kent.
From '65 to about '80 were very cool days for RVs, as there wasn't the huge degree of standardization we have today, and a lot of companies that didn't have any experience with them decided motorhomes would be a good thing to diversify into. Clark was principally a forklift manufacturer; one of the weirdest was FMC--originally Food Machinery Corporation--which made a racy rear-engined luxury 29 footer that cost as much as a house. FMC ended production of the motorhome when they got a big contract to make the Bradley Fighting Vehicle.
Anyway, enough pedantic history. If you haven't already, go here:
http://www.cortezcoach.com/
for the useful owners' group link.
Just one observation, though . . . at better than 40 years old, and pretty esoteric even in the day, purchasing this would be better viewed as getting a cool hobby rather than transportation. They were built for a less-crowded, less-frantic time and driving the 225 six version on a freeway may be borderline scary. No safety features, modest brakes and pretty slow. On pavement, it wouldn't be conceptually too different than driving around a Pinzgauer or small Unimog. Which isn't to say that it's bad, just to say that it won't be normal progress.
And another observation I've personally come to from my experience . . . motorhomes are not generrally constructed for off pavement use even if their chassis can manage it. Long stretches of washboard, particularly, can make cabinets fall off the walls, wiring coming loose, etc. Plus all of your stuff gets bounced around pretty bad. The Cortez is among the very best constructed of motorhomes, but even so, don't expect solid, rattle-free off-roading. It may well drive like it's shaking itself apart.
A Google web search will get lots of pictures, or you can see a fully restored one here:
http://64cortez.imagins.com/1964_Cortez_Motorhome/Welcome.html
including this illustrative picture:
.