Not that long ago, (maybe a decade ago IS a long time ago) I bought a 1984 p30 stepvan that was professionally converted to LPG when new.
I knew this guy who was my Rasputin. He could talk me in to anything. He convinced me to buy this to be my hill climb racecar hauler. BTW, I used to make money and though the spitfire he was helping me restore & the P30 ("Connie") was how I could start racing. This was before crapcan racing was around, but I digress....
The truck ran when parked at MIL's. BIL hates Connie and wants to strangle me because I still haven't gotten back to a place where I have time OR money to work on it or get it out of his hair.
The tanks are as old as the truck, there are 2. One is full, one is mostly full and leaks a little.
I've searched online and haven't found much info on early '80s Chevy trucks with propane beside conversion info or stories about people's experiences with Propane or why you should or shouldn't go propane, etc.
I've had fresh batteries hooked up and cranked for aloooooooong time before, but that's about as far as I've gotten, honestly.
Why did I NOT ask the germs to "learn me" about how one resurrects a beast like this?
As a prize, you can have my undying gratitude AND my rusted-out 1967 mgb (title like floors, none) for free! Or if that's not good enough for you, you can choose to have nothing to do with same said scrap, same price!
(grm'er I was typing but respectfully, I kinda like germs)
with love & respect.....e
*not "that" kinda love, he didn't try to convince me to do that. 
