There is no corrosion like that on my 535. I've been under there a few times, & all the fasteners are clean. I replaced the fuel filter last week & checked all the lines; they're rust-free. When I put the 3.64lsd in the car, it was easy to work the fasteners with hand tools. When I put Bruno's subframe inserts in, that hardware was clean too.
I suggest ya check the hardware to the gas tank straps, remember Scott H, or somebody out East, seeing those fail, allowing the tank to sag.