Ok, I solved the problem. Shucks Auto had a rack of generic thermostats. They are sized by diameter. I took the OEM thermostat down and found that a 44mm one is identical and come in 180f & 195f. Alaska, being on the cold side, I went with a 195f. Ran the engine for 15 minutes at 2000rpm, no load, and it came up to temp and the cab heater really put out the heat. All radiator hoses got almost too hot to hold my hand on for more than a couple seconds, about the same as our 2 vehicles with 195f's installed.
I really think that in the colder climes, a stock 160f will keep the oil from getting up to a proper operating temp causing sludge & acids to build up. Also, I read somewhere that fuel burns cleaner with warmer engine temps. My Izusu 4cyl 60hp diesel in our 32' boat always runs around 190f under load and drops to 180 at idle. After 1000+ hrs on it no problems.
I do believe a temp gauge is in order though.