Good thing to protect and preserve the Miyata! 1st because it is a great ride of course and 2nd because to inform future generations on how a proper bike has to be built.
Anyway, I did a lot with rust prevention. I not only treated my classic Saab, but also all my steel bikes with Mike Sander and/or Fluid Film.
Mike Sander is a bit more hassle to work with. It is grease that needs to be heated to 100°c, you need a compressor and professional spraygun BUT your bike will be save for at least the upcoming centuries.
FluidFilm AS-R is very easy to work with. It is a thick oily substance that comes in an Aerosol can and various nozzles are included or available. Still a great method.
I never used JP Weigle, because it is not available overhere.
