In addition, look for a plug up underneath the powerhead at the top of the leg -- looks about like a lower unit drain plug, if your model has it. If you take out the plug you can use the opening as a flushing port -- take it off briefly while the engine is running, and you should get a strong flow if the pump is working. The plug is situated up at the end of the water tube.
The ports on the leg varied a little in style. I believe my '57 ports on the sides, not the rear. In any case, it would be worth running a small wire or tube in to clear -- a little carb spray can sometimes help as a solvent, using the plastic nozzle. They get blocked up, particularly with salt water running. (But don't spoil the paint with the carb cleaner.)