Replacing Rear Spring U-Bolts?

[8EL]

I was going to mount the rear spring on my coupe today. I had purchased new U-bolts, brackets, nuts and carter keys. However it appears that the U-Bolts were installed (probably was a rolling chassis) before the body was installed. There does not appear to be enough clearance between the floor pan and the cross member to remove the bolt for replacement.

Is there some trick to changing out these fasteners? Has anyone done this on a coupe without either cutting access holes in the floor pan or partially raising the body?

I am all ears.........