If you are looking for cheap then I think original is the way to go. Post a wanted add in the swap meet section, you may even find one someone is giving away.
Problem with any frame newer than 54 is the axles got much wider, and the tires don't fit under the front fenders.
I don't know the differences in measurements for 46 and the AD trucks, but I would think that would be as close as you will find for something that may work and not be original.
Problem with swapping frames is you have to make everything fit, cab mounts, radiator mount, brake pedals, and steering column just to start with.
So, because there is no modern frame that will even begin to simply swap under your 46, and the next body style newer is still a lot of work for not much benefit, I say stick with an original frame.
My truck has the original frame, not much else is original, but the frame is, as it fits under the sheet metal like it was built for it, and is plenty strong for what I need. It also looks right, like it belongs under a 48 truck..
Grigg
