Hi, Looks like you will have reduced the weight of that rig by a ton Or more just dumping that timber tray.
Before the scrap man gets the Upper steel frame just check it out for dimensions as it looks like the back 2/3 of another CMP mounted upside down,
If it is then you make be able to get a couple of good repair sections from it to rebuild the Truck chassis to a Standard wheelbase.
There are a couple of recognised ways to cut and lengthen/ shorten chassis that give a strong joint and will be as good as new, A straight top to bottom cut, to give a square end profile is one way then cut the donor chassis to match .Weld together and then add an internal Brace [flitch plate ] [fish plate] not forgetting to >_< the flitch internaly to relieve stresses.
However, many years in the truck industry and having seen this done by experts. cut the truck chassis at an angle [sorry do not know the number of degrees ] but at a guess 45 degrees. Then cut the doner frame to match.
A good FLAT FLOOR, a SET OF STRONG AXLE STANDS TO SUPPORT BOTH HALVES of chassis, AND most important lots of Steel angle to clamp all the bits SQUARE.not forgetting to measure the diagonals to make sure that it is not only level but parallel. TACK weld all the brace bars in place before attempting to weld the halfs together.The true advantage of this join, known in the UK as a SCARF joint is the length of the weld on a slope is far greater than a top to bottom joint. Much more substantial and Permanent, stress of weld is reduced as it is spread over a greater length.
Finally an insert flitch plate complete with cut aways to further reinforce the repair fitted on inside Also >_____< to relieve stress on the road.
I personally cannot weld and I would be happy to give this sort of work to a Qualified welder, Although it may cost a bit more but will leave a ready to roll tidy join and safe chassis for your Rebody project. One that you can depend on on or off road