swb frame rust question

[kanuck]

Whether I should of or not I ended up making a deal for a ex project that is some what rough. The cab has new rockers and cab corners that are put in terrible and not near straight, and the floor patch is welded right over the old rusted floor. Has a slope nose hood which is OK and a 67 GMC front which is rough.
The main item is the swb frame which is straight, has new ball joints and a few other front end pieces, is sand blasted and painted, has a 5 lug disc brake setup, 12 bolt truck rear with 5 lug on trailing arm suspension with straight non rusted arms.
The bad that I found is the lower rail of the frame has heavy scale/rust in the section just above and forward of the rear end where the two plates are rivoted together. can this be cut and repaired? or get a frame section to lower the frame and cut the whole section out? What is a proper but not too expensive solution?
He wanted $350 for the frame, $400 for the cab and $500 for the front end which was out to lunch, but I am getting the whole thing for $400 and hoping to sell the hood and a bit to lower the frame cost for a future project.