How crucial is a thermostat, really?

[Cap'n Hook]

Today, I decide it's time to replace all the coolant hoses and the thermostat. So I flush the radiator and take off the thermostat housing. And to my amazement, there's no thermostat!

Bought the truck from a guy in Waco about 18 months ago, he never mentioned it needed one. And I drove it all summer last year, and it made it through one of the hottest, driest summers we've had in a long time. I had always watched the temp gauge start edging up towards the 200 mark, but just figured, the thermostat was stuck open. Never would have guessed it wasn't even there.

Tomorrow, I'm going to pickup all the new hoses, cap, and thermostat. So, any ideas as what part number is for a GM Goodwrench 350 for a 175 degree stat?

Actually, a little bit of me, last summer, wanted the motor to cry uncle, just so I could give the wife and excuse to go through it!