Are vintage Gillettes considered substandard equipment for method shaving? Everything I see indicates that Merkur HD's and the Progress are the razors of choice.
Yes you can use it so long as it is a single blade shaving (ex: DE, or str8). One thing about method shaving is you can customize however you want. There are no strict guidelines if you don't want. You can do your own forms (passes), use your own steel (razor), make your mix (lather) how you like, etc.
Your title said Gillette and I'm glad your not talking about cartridges or disposables. Either of those would not be acceptable with the method. Those shaving devices are only acceptable with traditional creams and soaps.
I'll admit that I don't know what goes into the method shaving process, but why would cartridge razors or disposables not be acceptable for method shaving but be okay for traditional creams and soaps?
I can't imagine that the process of putting a blade to your face is that different with method shaving, that it would work for one but not the other.
"Indeed, in the century since its appearance the 1904 "classic" has never been withdrawn from production. Once produced in America, it is now offered in an excellent form by the German company Merkur. Today, it is available in what is universally known as the "HD Standard" double edge razor. It is this razor--and this razor alone--that forms the basis of all modern Method Shaving. In short, Method Shaving is defined exclusively by the use of the 1904 model, "fixed blade" double edge masterpiece."
-Charles Roberts
This is why it is confusing. CAR seems to state pretty clearly that the HD is the implement for Method Shaving. So would shaving with a Fatboy or Superspeed be a bastardized version of method shaving?
Charles has told me that it's not so much the razor but the blade that makes the difference. He used to recommend feathers. I don't know if he still does though.