Get ready for a flood of coolant in the cab. That 1950-something heater core isn't going to play well with the 15+ PSI cooling system pressure of the 4.3 L engine. Either drop the radiator cap pressure down to 7 PSI, or rebuild the heater with a modern core designed for today's pressures. A lot of the S-10's had a hose nipple built into one of the radiator tanks for the heater return line.
Jerry



"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!