47-55.1 Frame Shortening on a '50 1-1/2 ton?

[Blue'66]

Just bought the above mentioned truck. Pretty solid, running condition, has a flatbed on the back that supposedly used to dump. The flatbed is about 11 feet long. What I want to do is shorten the truck and put on a 8 or 9 foot dump body. Does anybody have any ideas on what is the best way to go about this? A buddy of mine says to move the rear axle + springs forward, and chop off the excess frame. Only problem with that idea is loosing the slight notch out for the rear axle. Is is possible to cut the frame, and re-weld it together. I was kicking around the idea of cutting the frame in a way that it could fit back together, like notching it, weld that seem, and fishplating over it to strengthen it.

I've never done a frame shortening before, and any ideas are greatly appreciated.
Thanks all