I don't have any experience with the lenses you have but I would guess the Chinon will serve you well. Do a quick search for that lens and see if you can find any reviews done based on its use on a DSLR. The 50mm designs are well established and have had plenty of time to evolve. Don't worry too much about coatings. I have both coated and uncoated lenses. Each has a special flavor. Not one is "bad" and not one is "good".... although I adore my FA 50mm f/1.7!
Why not keep both bodies? You can get very nice SMC coated 50mm primes for $20-$50 on eBay in both M42 and K-mount. Run 200 film in one and 400 film in the other.... or get a 35mm prime in one mount (or the other) and you'll have a wide-ish angle lens on one body with a normal view lens on the other. Possibilities!