OK, progress report.
We found a level parking lot to see what was the extent of a "disagreement"
between 2L truck, ET Jr. and a SpaceCraft.
About 4 1/2 inches of disagreement. Several option we discussed and considered, from minimal to "very radical" and we settled on an compromise solution. Modify Marsha's 29,000 lb box.
The box was cut down and new base plate and a new pin were welded in.
We modified the "original" a bit. The original had 3/16" pin plate with an inch reinforcing backer. We opted for 1/2" pin plate and a 1/2" backer.
Also the pin is double welded, an internal chamfer (between the plate and the backer) is filled with a weld (then there is the top weld).
Robert did FEA analysis and "the fix" is roughly equal in strength and stiffer.
The unit is currently hanging in the "paint shop".