Any tips for saving this poor thing?

Nope, it won't hurt the finish, but it does have two properties which are really useful - it has an astonishing capacity to soak into tiny spaces, and it will dissolve small rust crystals along with old oils and greases and pretty much anything else. Once you get the gun apart, you'll have various chemical options to stabilize or remove the remaining rust, but all of them (to my knowledge) will remove the remaining finish too. The only effective way I know to remove rust that preserves the finish is brass or bronze wool, I've used it before with good result. If there is rust inside, pay attention to critical bearing surfaces (sears, safeties), springs, and of course the bore and chamber. A pitted bore might or might not shoot pretty well, a rusty chamber might or might not cause extraction problems. If you're lucky, the bulk of the pitting is outside where is just adds character.