Re: 1960 Merc 300s Water pump removal
Is the pump cartridge itself damaged? Generally, unless the pump cartridge is really worn, I just replace the impeller. If I need to pull the cartridge, it usually means I'm pulling down the whole lower unit and the easiest way to get it out without breaking it is to pull the whole driveshaft out, pulling the cartridge with it. The driveshaft is bolted to the pinion gear, so it will not simply pull out. You would need to pull the gearcase apart to get at that.
Unless... you're simply trying to remove the cap, in which case you can either fabricate a tool out of some aluminum bar stock (not difficult if you have a drill press) or see if you have a local old-time Merc guy who has the special tools. Others have used spanner wrenches with varying degrees of success. I bought the special tool off eBay a number of years ago and it certainly makes things easier...
