I recently acquired an antique floor safe marked for the Lehigh & New England that will be going on display in a climate controlled building. The safe is in "fair" condition at best, and while it will be stored in a more forgiving location than it was previously, (in a garage under some welding supplies) I would like to do something to it that will make it a bit more presentable, preserve the remaining paint, and prevent the existing rust from spreading. I was considering using the boiled linseed oil trick, but I've heard that that may damage the paint in the long run. Any suggestions?

I don't think the linseed oil would have a detrimental effect on the paint itself, other than taking a while to dry to the touch, although I think it's more for porous surfaces like wood, not steel.

Your safe is hopefully in better shape than this Katy railroad safe that was "cracked" by burglars in one of their rural depots back in the 1969!

If you look at the top of the safe's door frame, you can see it lettered MKT RR. The local sheriff in the picture is dusting it for fingerprints.