In Washington the law says that if your load weighs more than 40% of your tow vehicle you must have working brakes on the load. So to legally use a dolly with no brakes your towing vehicle would need to weigh at least 12,500 pounds (2.5 times 5,000).
Washington Towing Brake Law Empty with no bed that truck weights somewhere between 4,100 and 5,500 pounds. A grain bed is going to add at least 1,000 and maybe 2,000 pounds. If it was used to haul grain you might find some old weight slips in the cab that would actually say.
'49 2-ton weight People are going to argue that its safe and they do it all the time with smaller pickups or cars. I take the other side of that argument. Its both illegal and NOT safe.
And in Washington the law takes a punitive attitude if anyone is injured or killed since something fell off a trailer a few years ago and destroyed a young girl's face.
Rent a trailer long enough to load and distribute the weight of the entire truck, make sure the trailer brakes work, and use a large enough truck to tow the trailer that you aren't endangering those around you.
I'm surprised a grain bed in Eastern WA would not have a hoist and a 2-speed.
Does the valve cover have four bolts around the lip holding it in place? If so it sounds like a '54 or later 235 or possibly a 261.
There is a FAQ on posting pictures on the first page of the forum, that should help you get some photos here.
