Re: 73 evinrude 6hp water pump replacement
Essentially its just a question of dropping off the gearcase. The pump is mounted on the top of it. However the shift rod is in two parts and the joint between the two has to be undone. Not sure if that accessible once the gearcase is lowered a bit or if there is a rubber plug on the leg to access it (the former I think) I also notice that there are a lot of bits and pieces at the top of the drive shaft on this one.
You may just need an impeller kit or you may need a pump repair kit. the later contains just about all the parts of the pump and a new drive-shaft oil seal.
THIS DIGRAM shows it all and all the parts of the gearcase as well!
The acquisition of a manual would be an advisory first step.