You can use the deluxe switch.
The recirculating heater in my '57 GMC had a little flap right at the end of the duct that forced air to the floor. When the flap was shut it forced air up the defrost hoses to the defrost vents that bolt to the underside of the dash. I don't remember that there was anything to cut. I think (but wouldn't bet my life) that GMC and Chevy used the same recirculating heater, maybe with a different label.
Anyway, I think all you would need was the vents, a recirc heater and a few feet of defroster hose (available at any FLAPS).