These are the last of the Mercury built Wizards & carry the MK-25 "detuned" powerheads. What is interesting is that some of the 55 WM7's carry the Mercury MK-20H needle bearing center main cranks, albeit with a 4 cage reed. Some of the 56 WM7-A's carry the MK-20 Block with most of the pads machined out (but not all). These blocks retain the 20H porting & are easily recognized from the outside if you study them. The 55 WM7's with the 20H cranks are NOT evident unless "torn down" . Also some of the 55 WN7's Powermatic 12 shift motors also carry these parts as well as the 56 WN7-A & I have been told that some Powermatic 12's also carry the MK-20H flywheel. As I have not purchased any Powermatic 12's I cant confirm that but I have found two Merc 20H blocks on Wizard WM7-A's original motors with matching serial #'s (Wizard #'s). I have confirmed all of this thru observation as well as directly from Charley Strang & the reason for it happening. The insertion of these Mercury racing parts into these last Wizards, (only could have happened after 1954, which was the time period of the run of the 20H motors), seems to be in a random pattern rather than in a certain block serial range. By the way, all Wizard Motors were built, tested & boxed at the Mercury plant as Wizard did NOT have a mfg facility but rather only a distibution capability All very interesting facts made available by MUCH research.