<font color=blue>...Quoted a price of 54.00 for thermostat...</font color=blue>
Ouch...! /w3tcompact/icons/crazy.gif
I'd try using a caliper and measuring the old one or taking it down to a NAPA store and get it matched up.
Worse case run the unit without the 'stat and if it still overheats within 10 minutes... you can eliminate that rather quickly... /w3tcompact/icons/eyes.gif
Use a pressure pump (with a readable gauge you can observe) that clamps in place of the radiator cap, pump up to the specified pressure and check for leaks and also it should maintain this pressure for a period of time without loss...
With the unit running and the radiator cap off... after it's warmed up ~say your 10 minute time frame, grab the top radiator hose and squeeze it shut for a couple moments and release... you should be able to see a surge in the radiator and also feel the hose "pulsing" if the water pump is working properly... Again, if worse comes to worse, take the pump off and inspect its impeller and spin it with your fingers...
Sometimes you can take these parts down to a local NAPA or long time auto parts store in your neighborhood... an 'old timer may be able to look at the component and quickly ID it or get you in the ballpark.
You can check your exhaust for "water", check your oil pan for "water" in the oil, signs of a bad head gasket, cracked head, or cracked block, etc...
Some of the prices charged for these parts are an absolute Sin... It's beyond common logic why some prices are what they are... /w3tcompact/icons/frown.gif
Warped heads, bad head gaskets and failed water pumps have been a problem with the Mitsubishi engines in the past from what I've been told...
I wish ya the best... Good luck... /w3tcompact/icons/smile.gif