its a full frame, and these are prone to rot from inside out...I spent about a year under mine. Hopefully yours is nowhere near as bad as mine was. I did see some pics where a frame shop dropped the frame straight down to replace the siderail, but looked difficult- somehow they dropped the entire frame straight down with front clip still attached to the body- looked easy to bend something...lots of stands. I'll try and find a pic of that guys car, not sure if on this computer. you *might* get a frame shop to patch whats there without removing body, but I doubt it these days...if it ever broke they could be liable...patching from bottom dont allow much strength. I honestly dont know if frame guys will even weld on a frame anymore...best bet would probably be getting a rustfree frame from out west and swapping out- just be sure donor frame is clean.
heres some pics of the mess I had a while back...anyone in their right mind woulda scrapped it...
holey frames batman!
heres the part I kept:
rebuilt- side rails from 2x4x.25 wall tubing, rear arches and torque boxes fabbed from almost a full sheet of 3/16...
or if youre bored the long storys here: