Holley 1920 R-4003B, 4162

That throttle plate anti-ice system was standard equipment in '69 (only) in the USA; optional equipment in Canada from '60-'68 and standard in '69. Not used in North America after '69. Info on that system is here. Today's gasoline almost all contains d'ethanol, so your throttle plate certainly isn't going to ice up, and the anti-ice system heats up the carburetor something fierce and makes driveability problems.

Best to bypass the metal tube that goes through the exhaust manifold to heat up the air, and install an appropriate hose barb-to-invert-flare brass fitting in the throttle body. Run vacuum hose from the fitting on the underside of the air cleaner directly to that new hose barb. This way you don't screw up the carburetor's idle (which is calibrated with the air coming through that port in mind), and you stop the carb being turned into a teakettle by the unnecessary heat.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.