Howard,
I never had to get into the thermostat or even the cooling system on mine so I'm at a loss to help. I'd love to see some pictures though. Since we can't do pictures through this messaging system please send them to my direct email:
neil@duttonengineering.com
My Perkins had the header tank on the front of the engine above the belt, I think yours is on the port side. My HX was transverse across the back. What spares were included?
Do you have a manual?
http://www.manuals.us/westerbekedies...viceparts.aspx