Your 1941 Wizard single(to the best of my knowledge) has a "rotex" hockey pucktype water pump. Reproduction pucks are available from several sources.
Oliver Outboard site lists price and availability
for various makes and models including yours.
It is possible to install a postwar vane
type assembly in place of the earlier type(Mercury
offered a kit too). Any Mercury single thru KE3
is a direct swap (gear and all) Any Mercury twin
thru KD4 is a swap except for gear. Same can be
said of Wizards. Simple to remove entire assembly
by taking out the two bolts...sometimes due to corrosion and crud taking the assembly appart can be a task. Have done several Mercury, Wizard and Sea Kings of this design. They can be an adventure or
routine...you know after you get there.