It appears to be the same model as the one below with leaf springs and a heck of a solid frame and heavy duty axle (the solidity of the box could be another story though)
To answer your question, what is your end goal for a trailer? Just a cargo box or more?
It looks like it could be an interesting project... push the lid sections to the front and rear, build a middle section, side hinge the lid and build a read door, there is possibility there... how much experience do you have in fabrication and such? How much to you want to learn it?
I'd try to talk him down... the tires are probably trash, bearings need regreasing, body needs a LOT of work to make it into what you want...
Have fun!
