What setup are you running?
If it's the '69 and earlier iron water pump (driver's side inlet), just take out the heater nipple and screw in a pipe plug.
If it's the '70 and later aluminum pump (passenger side inlet), cap it with a rubber cap and hose clamp. Or, you could try something like this from Speedmaster, that doesn't have the heater or bypass: PCE® Water Pumps, Mechanical PCE195.1108 | Buy Direct with Fast Shipping (speedmaster79.com)
There's others, too- I'm thinking Edelbrock and Milodon, maybe Flowkooler...