Don, I do a fair amount of work on old stuff (2 '48 two ton dumps, tractors etc.) I'm also saftey officer for the town F.D...by way of saying that the cardinal rule is ask yourself what is the absolute worse thing that could happen, and assume it will. BLOCKING! Get yourself some 4' 8X8's or some rugged jack stands, the heavy duty kind, and crib the frame. Rig it so that the tires/wheels aren't what you are depending on the hold the truck up and stable when you crawl underneath.
