I think you'll find "see-saw" to be even more of a problem than reels for film that's been on the roll for seventy years.
For the 1950s slide film,
Rocky Mountain Film Lab advertises that they process old film of all kinds -- but like other labs that handle old film (Blue Moon Photo in Portland, Oregon, for instance) they'll generally process the film as black and white negatives and then attempt to retrieve the image by scanning. Problem with that is that many old color films had a silver filter layer, which will show as heavy fog in B&W process, making it very hard to recover the images. It's likely you'd get equal or better results processing the film yourself, in B&W chemistry, but then very carefully (by inspection) using Farmer's Reducer to bleach away the silver filter layer (and fog) just until the rebates (mostly) clear.