Let's level-set: pretty much any RV is going to be a money pit, it's really a question of degree and mitigation. ;D
First off, is it a Ford chassis with the 351W (which I think most Ford people refer to as the 5.8 but that might be a US/SAE vs Canada/Metric thing) or is it a Chevy with the SBC 350 (5.7)? It probably doesn't matter too much one way or another, but good to know regardless.
That age will be a carbureted engine which will provide less power, lower efficiency, and require more maintenance. Or at least different maintenance. I'd set my expectations at 6-7mpg (40-47 l/100). A newer C could have the potential to do slightly better than that. Before the carb people come out of their caves to beat me, I will admit that a well-tuned clean carb will get you plenty of power and be efficient, it just takes more work and knowledge to keep them in good nick, versus injection.
Also understand that there have been leaps and bounds in terms of quality and longevity in mechanical parts in the last couple decades and '83 isn't really part of that. Newer engines (starting in the 90's but really accelerating at the turn of the century) can run for 100k properly maintained miles and not show any real signs of wear. SBF or SBC from this era will show wear and, quite frankly, will just wear out inside. Not saying it's a ticking time bomb mechanically, but 1983 was a really long time ago in terms of build quality. I would absolutely check compression and leak-down numbers.
The chassis, however, is probably the least of your concerns. It's really just a regular old van under the covers so it's a pretty well-understood system that anybody can fiddle with. It might require a shop with the right type of lift, but you're not going to need any crazy-special skillset or tools to be able to diagnose and work on it, and parts availability should remain fairly strong.
Moving on, though, we get to the home part of the motorhome. That's the tough bit. The appliances, electric, plumbing, furniture, roof, and basic structure have seen 35 years of weather and road vibrations. My regular house was built only 18 years ago and it requires regular maintenance to make sure it doesn't fall down around us. It might not be the best-built house, but when they were choosing materials, they didn't need to think about trying to keep things light enough to fit in the constraints of a van chassis GVWR. To make things light you can do one of two things: use very strong, very lightweight, very expensive materials -OR- use smaller amounts of regular, cheap, heavier materials. This ain't no jet fighter, so think thin, weak, and cheap. That's not much of a problem as long as things are well maintained, but that's where 35 years starts to catch up to you.
It is almost a certainty that there has been some water intrusion at some point. How long before it was fixed? How long before it was even noticed? What was done to remediate any structural damage? Is there rotted wall or floor? There is some metal frame present -- was water kept up against that, causing rust? Did mold grow and if so, was it all abated? Water damage in an $85,000 coach is not much different from water damage in a $10,000 coach, but there's a big psychological difference between paying $5,000 to properly repair a coach worth $85k versus one worth only $10k. Or paying $1,000 to maintain a $85,000 rig versus dumping $1,000 in maintenance on one that's only worth $5,000. They both might need it, but the cheaper rig will seem like good money after bad moreso than the expensive one. An older, low-buck vehicle is just much more likely to have deferred maintenance and incomplete repairs.
If you are the handy sort and can be a mechanic-roofer-carpenter-hvac tech-appliance repairman-plumber-painter-upholsterer-electrician and you're starting from a solid base, then buy it and you're going to have the time of your life. I'm that kind of handy sort and enjoy tinkering, fixing, and improving, so that sort of thing appeals to me. I know of a guy who bought a 1940's or 1950's school bus that had been converted into an RV then fallen into complete disrepair, drove it a few hundred miles home with his son, and is in the process of revamping it including possibly swapping in a newer diesel drive train. Great project. But if that's not your thing, I would probably avoid this one. If you have to farm every repair job out this thing will just eat you alive.
There is a remote chance that this is the one that has been garaged, has perfect maintenance records, never had any leaks or other structural damage, and is absolutely cherry and ready for another 35 years, and if that's the case go ahead and snap this thing up and enjoy it and share your epic tales of adventure! More likely though, it's an average unit that needs a bunch of things and will be a good amount of work. Now, if that's what you're looking for please, by all means, snap that up and share those epic tales of adventure. But more than likely, you're looking for something that you can get in and use without putting a lot of money or work in to, and I'd hate to hear those epic tales of woe.
