I might need some info from you! I just bought this truck last week!
http://imgur.com/a/Jx2lu <-- pics I took with the original (hippie) owner as I was buying it
http://imgur.com/a/lPsws <-- pics she took when she offered it to me
It's a 1982 Grumman Olson Kurbmaster (GMC P30[?], Chevy 350v8 propane fuel), I've been doing a lot of research and apparently I can get any parts I need from stepvanparts.com, which I'll be making my first order this week: replacing EVERY light with LEDs!! The thing runs and drives perfectly fine, after sitting for 5 years we were able to turn the key and drive it 2.5 hours home to where I live. I am absolutely in LOVE with my Grumman!!! It is going to be the center of attention sometime in the near future, It's going to be bitcoin-powered by the time I get finished with it!
If I could get a Kurbmaster service manual I would pay a premium for it, I've looked around and they are tough to find if not impossible. It's basically an RV chassis, so replacing parts isn't exactly complicated, but there is a lot of things I am clueless about. There is a spot to put a gas tank, it was never installed at the factory but one would bolt right in, and I heard that I can have a switch and then toggle between gas and propane as I drive. How I would achieve this, I'm not sure, I'm a computer-guy, I know how to keep a vehicle running but I'm not a mechanic.
I'm not sure what to ask right now except maybe when I'm getting down 'n dirty doing the overhaul I might need a tech I can prod for answers. Oh, here's one: the truck right now has a 3-speed manual transmission. I love driving stick, but this thing isn't fun to drive lol. It has gears L-1-2-3-R, sort of makes it a 4-speed but the L gear is basically useless, you can only do like 1 mph and I guess it's for hauling stuff, or getting the truck rolling, it's pretty useless for regular driving. I would love to slap a new trans in there, I was thinking a 700R4 4-speed automatic would be excellent for cruising, plus the overdrive gear would give me much better milage, since the current trans only lets me get up to about 80 kph / 50 mph. I know the 350 will love having a new transmission mounted to it, but will the new transmission be strong enough to take the weight of the vehicle?
Also, since when I hit any bump, this thing makes so much noise in the back, I think if I were to upgrade the suspension to air-ride it would be a nice cushy ride. Do you think I could get a good air-ride system installed for ~$2000?
Haha. Your enthusiasm for your Grumman is oozing off the screen
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Because of how old it is, I'm not going to be much help, but here is what I do know. You are right, the engine would love a 700R4. As far as whether or not it can handle the weight, absolutely. It should do it without any modifications except an external cooler. After the install, you will need to install a system to control the electronic torque converter. They usually have kits for that kind of system consisting of a vacuum switch and a new brake light switch, and I can talk you through that when you're ready.
Re: Service manual, I don't have access to one. But surprisingly, my information database does have diagrams and other technical info for the 1983 model year. I could compile a PDF for you if you'd like.
Re: Gas conversion. I'm going to stay out of that one. I've never touched a carb in my life
Re: Suspension. I'm staying out of that one too. I'm an electronics guy, and I know what I don't know, and I don't know suspension options
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Feel free to come back and post any questions you have along the way.