Here is an important link to a Mercury outboard price list I uploaded that has a cross reference of old part numbers and their new corresponding part numbers beside them.
To convert an old Wizard number to old style Mercury number you simply change the "W" in the part number to an "M".
For example, the Wizard drive shaft W-50-186 becomes M-50-186. Look it up in the price guide and the new mercury number becomes 45-24449. You now have a valuable tool for finding the NOS part on someones dusty old shelf. Most old parts are still very difficult to find, but at least this is a start.