is this an eames chair?  

Too tall
The one physical difference that I think I notice, is that the back seems to be a bit taller than an Eames shell.

I would NOT give up.
Even...
I would NOT give up.
Even if it turns out to not be an Eames piece, the story could add much to the value.
Where was it found? If it was in West Michigan?
I have worked for several years with several office furniture companies and have had access to many prototypes.
Often these items are stolen, given away and enter society.
I've seen rooms piled with prototypes.
I think people here should know that a simple chair can spawn hundreds of mold concepts, leg shapes. etc. Companies often mock up several nonsitable full scale models just for a furniture show only to have the parts cannibalized to build revised versions. I have known engineers who have taken home discarded chairs and simply used them in their garage or hunting camp to avoid wasting them. Prototypes aren't special or valuable until recently.
NO ONE can say say this is not a Eames prototype unless they can PROVE it is not by actually showing it being developed for a separate purpose.

Questions remain.
While I would certainly defer to Tynell's specific knowledge of all things Eames, it seems the scope of his curiosity regarding this object is limited. And rightly so, perhaps.
It's obvious to me that the piece exhibits evidence of skilled craftsmanship. The question that recurs is why anyone would bother to invest the thought, time, and materials necessary to, in effect, reproduce a commonly available item?

Stick with Eames, Ty.
And try to keep in mind that the opinions and advice we offere here are completely commensurate with the price of admission.

freedomBigelow, Please...
freedomBigelow, Please contact us as we are very interested in purchasing the chair from you. You have something very special and would love to add a missing piece to the story of Charles and Ray Eames.
(edited by DA)

Intelligent Design?
Where is tinyarmada when you need him (them)?

Tynell.
On this we can agree. That cracked me up, too.

a little update...
got a response from HM stating that the base might be a variation of the original X-base and they would need more information to determine its origin/lineage.
i don't feel i am wasting my time investigating and researching on the chair since i am having fun doing so and learning a lot along the way.
by the way, the chair was acquired from someone who received it as a gift in the 50's given by his friend who is from michigan.

There is more...
I've found this ebay listing. This won't help much, I know. These are also from Michigan.
http://www.ebay.com/itm/Vintage-Herman-Miller-Ames-Style-Fiberglass-Shel...

Do you happen to live near...
Do you happen to live near Oklahoma? I have bought in the past a set of fakes that were so close that I would have to assume that Herman Miller may have had to send this company a cease and desist letter.
Mike

Plasti-Co chairs were...
Plasti-Co chairs were produced here in Oklahoma City. They had the same style of fiberglass, and also an X bases. The base on my chairs where covered with a layer of fiberglass, maybe as a reinforcement.
http://www.flickr.com/photos/illtakeyourphoto/8475901441/in/photostream