Hello!
Welcome to the madness from Salmon River Country!
Very cool set-up there. I have a 1945 Ward LaFrance M1A1 Heavy Wrecker equipped with that style crane and it is proving to be pretty handy.
Just so you know, that Garwood crane has it's own manual. TM 9-1796. "ordnance maintenance: crane assembly for heavy wrecking truck"
The TM 9-796 manual is for the whole truck (WLF) but has LOTS of info on the crane and is out there as well.
View attachment 827876
Once in a while they pop up , but seem to be pretty rare.
Just remember when using those control levers to throw them with authority. Snap in and snap out. DON'T try to "feather them".