Gary,
Very nice find. Although the grips are beautiful, you're probably right that they are a little late. I have a 6.5" M1926, sn 29333 with the correct numbered convex non-medallion grips and it shipped to W&K on April 20, 1927. You're also correct that the 6.5" M'26's are scarce. I was really proud to have found one, but to find one at the price that you did is almost obscene. (I could tell you how much I paid for mine but I won't. It would only add to your glee and keep me awake tonight
).
Good to see you at Tulsa.
Bob