Is the tenon diameter the same on the Montana 99 Action as the Model 70, one inch before cutting threads ?

Should be.. Here's the relevant page w/info:

http://montanarifleco.com/?page_id=258

I looked at the Montana Page before asking the question , it gives the length but not the diameter

That spec page lists the barrel tenon diameter as 1.0-16 UNF 2B

Yup - the OP missed it the first time, apparently..

Thanks, i did miss that when i read the spec's. I guess i was thinking it was 16 threads per one inch .