It is a mod to the thermostat housing not the pump. It is a simple thing to do and Indmar has the data. I you decide to do it, you will need the info from Indmar, thermostat gasket, sealer, and get a thermostat and change it while you are there. Te easier way would be for you to contact Indmar service with your engine serial number and get the proper parts from them. Ask for the price on a new modified housing too and that may be low enough for yto just buy it and swap yours out instead of drilling the old one.

As I wrote before, i have one that was this way from the factory and one a year older that was not. Never had a problem with the older one but upgraded it with new parts anyway.