Thank you Joe, a little clarification goes a long way. I will redouble my thinking that the hardware (all of it) needs to be preserved if at all possible. I second John C's opinion of Kroil.
I personally have had great success with PB Blaster. Many moons ago I acquires an old mobile home frame that had sat on the Florida coast for decades, and been flooded out by salt water storm surge more than once, I soaked all the studs with PB for three days, and a little persuasion with an impact wrench all the nuts backed off.
If neither of those work, an oxy/acetylene torch will generate sufficient heat on one side of the nut to expand the nut and break the rust loose enough to get penetrating oil in and get the job done. There is apparently an effort afoot to lengthen the car by 2 foot on each end. Getting the nuts off would allow a coupling nut with lock nuts to be used to extend the existing truss rods at a minimal cost.
FWIW
Bob C.