Dan Eubanks 626-827-4004 (Southern California) makes Model A cast water out let housings, both 28-29 & 30-31 with a temp guage boss on the drivers side to accommodate an overhead valve installation. He will drill and tap them for whatever size fitting you want.
If you want to see a photo of one go to
www.ocmafc.org. Click on tech articles in the left menu. It will pull up another menue of tech articles, click on Tom Endy's articles and scroll down to "Temp Guage Installation"
Some aircraft systems monitor both input and output to a cooling system. By pressing a button the flight deck can read the temperature drop across the cooler, which is termed "rise" temperature. I don't see a need for this on a Model A unless someone wants to monitor the efficiency of their radiator.
Tom Endy