Why not just swap your cab and sheet metal to a complete newer frame and running gear? Here in Tennessee older big bolts are just sitting around in farmers' fencerows, and a whole truck can be bought for just above scrap metal prices. You've got a cobbled-up mess already, and making it more of a Rube Goldberg situation with a hodgepodge of old and new running gear is going to be a nightmare every time you need repair parts. There's very little sense in trying to haul a load with a lowrider- - - -the suspension modifications necessary to lower the ride height make it impossible to use it like a truck.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!