Hey Gunsbrad,
You are in the right place. But there may be a better place. I do not want to run you off, but there is a blogsite called frontier folks.net or com. In that site they have a section for Native American impressions and those folsk are very helpful and may be able to help you more.
I have never seen an origianl in person so I do not know the specifics. The reproductions I have seen vary from the demensions of a finshed gunstock to the demensions of a rough cut stock blank which is huge. A buddy of mine has one like that and I will see if I can get details from him.
Now, like I said I am not trying to run you off, as you work on this we want to hear about it, and see pictures during and after construction.
Coryjoe