Unless your oven weighs a LOT more than it seems it should, suspension travel won't be an issue. You might even need to remove a few spring leaves to avoid beating things to death from the rough ride. I-beam is overkill- - - -space the bed up with a piece of 4" or 6" channel iron if you need to- - - -that's what dump beds, etc. are built with.
Don't scrap those rear wheel cylinders. They can be bored out and relined with brass or stainless steel, as long as the castings aren't broken.
Driveshaft hanger bearings should be a stock item at any professional-grade auto parts store- - - -NAPA, etc. They're pretty much universal regardless of vehicle manufacturer, and about 3 sizes cover everything from pickups to tractor-trailers.
Jerry