Frame bracing next to shock crossmember

[sick472]

If I had to venture a guess, these pieces resists the bending forces that the tongue weight of a trailer would cause and/or a heavily loaded rear section of the bed. There area also similar forces caused by hitting bumps that ultimately push up on the frame near their locations.

Replacing the cross member with a fabricated one may not serve the same function as these stiffeners. I'd put them back in, in some fashion or another.