Nice score Gary.... that is a Northrop unmanned target drone prop from about 1932-1963.... there were zillions made and became surplus after WW2 some time.... so that is prolly the prop that fits a Mac, which as we know was a drone motor
I reckon that one is prolly made between 1950 and 60, because that is when they made the most..... they got used up until 1980, but I reckon all the props would have been made at the beginning of 1950 So that is prolly what uncle Ivor used to get to put on the original Bensons
That, my boy, appears to be genuine gyrocopter history in your very hands!
http://woodenpropeller.com/forumvB/arch ... t-827.html
http://www.wmof.com/kd2r5.htm
http://www.designation-systems.net/dusrm/m-33.html
He used to get 1 1/4" timbers and saw them up the center then bond them back to back so each laminate had the identical grain crossing equal and opposite.... awesome craftsman.... hand made props will become a thing of the past soon 
I like the sensenich how they are hand finished 
