there was an article in a recent cornbinder connection about how many ih trucks end up with the wrong style of thermostat. many IH trucks used a thermostat made by robert shaw that had a special bypass design that worked with the water neck housing. not sure if the old sixes were this way, but most of the later v8's and slant fours were. here is a link to one:
http://www.shopih.com/NOS-860481R92-p-TS.htmlscottso, do you know if this would be the correct thermostat for an old six?
john