Wring 24 volt hazards
Welcome to Steel Soldiers and the pearly sounds of the 50's GMC 302 cu.in. sewing machine.
These 24 volt systems can weld metal if a guy doesn't chase all the wires before hooking that last wire to the ground on the last battery. There is some great info in pt 2 of the 9-8024 technical manual buried right here on SS between Upgrade and Rules.
http://www.steelsoldiers.com/showthread.php?106483-More-M135-TM-s
It's a little tough to navigate through the pdf manuals and much harder to take in the hot tub than the paper manuals, but you can still get them online.
I snapped a picture from 9-8024 pg. 292 but it doesn't clearly show the 3 wires that 'typically' hook up to positive side of the passenger battery from the starter and slave plug,,,,, it doesn't clearly show the wire from the negative post on the passenger battery running along the fire-wall, feeding the + positive post of the drivers battery,,,,,,and it doesn't clearly show the drivers battery ground to a point on the frame. Take a good look at the layout of your wires and just be real careful with battery awareness and the explosion factor.
I've looked at about a dozen motors and so far saved 4. They tend to stick the aluminum piston to the metal wall of the cylinder. I always pull the valve cover before turning any engine. We've found push rods popped out of the rockers.....they'll actually run like that.....and the previous owner would have assumed that the motor had a major problem. We re-set the push-rod and 4 years later I'm still running that motor.
Pull the plugs, add oil in the bores and turn by hand every year is the best advice I can give anyone that has an old army truck just laying around. Really hoping you get this one rolling because there's nothing like the smell of an Early Deuce in the morning. Best of luck and let us know what you need.