Yet another Eames Shell Identification Please  

Yep, indeed original Eames shells on stacking bases. (The shells before 1960 often had no embossment, but the date stamp and paper patent label are typical)
Stacking base shells have a wider mount, making them less interchangeable if you should want to put them on other bases.
There are aftermarket (non-Eames, non-Herman Miller) bases that fit the wide mount if desired, but these are not authentic and vary greatly in quality, and also have a bit of a strange look, in my opinion.
To some, the wide mount stacking shells are less desirable than the standard mounts, because of the lack of interchangeability. But if you like the look, or have the need for a group of chairs, they are a great design. A "purist" would probably leave them as is.
Some people will also move (or replace) the mounts to the standard (closer together) design. That might increase the value, but then the chair is no longer original "as found".
Anyway, nice looking chairs! Hope this helps.
EDIT: Sometimes the base screws are rusty and can be difficult to remove. Usually, they can be loosened up with various approaches, but sometimes they are rusted into the mounts.

Thanks for your response Eameshead, much appreciated.
The plan's to replace the stack base with the wide mount dowel leg offered by Modern Conscience. It hurts to separate the original base with the shell but the dowels would look so much nicer as they will be used as dining chairs.
I'm planning to number the bottom of the shell and original base with a small sticker should I want to revert to the original setup. Any thoughts on Modern Conscience? Worth the price?