I would go along with the diameter and pitch in the first listing, but the Merc super 10 (KF-7) has a splined prop shaft and would need a pin drive adapter which may or may not have been available in 1949.  The second listing is totally wrong as the KF-9 (25HP) was not available till 1949 and it was a 4 cylinder not a twin, and the prop shaft was larger that 9/16″.  Therefore, the only motor that it can work on is the KE-7 which has a 9/16″ smooth prop shaft.  It seems to me that a company like Michigan Wheel would have been more accurate in their listings.