From previous treads - it looks like a simple shutoff valve in the supply hose will work. I have plugged both hoses with no harm done . Just my 2 cents

Big Al

I'm going to be doing this myself shortly, too much heat from the old big block. Best to install a shutoff to the heater core so it can be turned on and off. I know I still need mine in the fall for the defroster.
Bill

You want to isolate the heater core completely, I run two ball check valves, one at the water pump and one at the intake

thanks, is a temporary fix until can fix heater control. they seem expensive for non stock replacement, $100. any other sources?

Hot cold lever broken