Where is a plug for Water Temp sender unit?

I can not use the electric temp gauge port due to it being a different thread. I purchased two Murphy gauges to install and need to locate a non used plug for fresh water side. Has any body added a mechanical temp gauge on a TAMD 41 D? I want to have a alarmed adjustable water temp gauge. The electricsender did not go off when I was at 210 deg and climbing. I changed coolant and oil and the engines seems to run a little cooler. I can run about 3200 rpms and temp stays just under 200 deg. I think that the stats are at wide open at 195 deg. Thanks for any input. Al