From the pics, I suspected a bent dropout hanger, not a bent cage, as the whole body appears twisted. From your description, the Suntour RD's mounting bolt is loose in the upper body. The bolt should have a corresponding slotted 'nut' that can be adjusted to tune out any play. This 'nut' butts up against the hanger once installed. There should also be a small screw to trim the angle of the RD in relation to the angle of the freewheel cogs.
Of course, the Suntour could have been damaged sometime in its past.
Looks like you have a Campy Super Record FD. Sweet!
If those SPD pedals spin smooth and have no slop in the axles, you're good to go, just buy some replacement cleats.
515's were entry level pedals, if they have signs of wear, toss them. To disassemble the axles requires a special Shimano spline tool.
You gotta tell me about this Goodwill shop.
