i have a 65 skylark manifold and carb. from the car im driving. "upgraded" to a edel. 4bbl 650... i saved my old stock 300-2, not sure why, but did. recently ive come across my "project 300" rebuild... same 300 motor, but its from a 66 skylark..but ive noticed a few things that are different...why? the manifold on the right is my orig. 65 skylark... the left is the 66... notice extra valve...and the "300" print. thats on the 66..
The extra valve is the heater control valve. Sometimes they're threaded into the manifold. The later style has two hose ends and get suspended by the heater hoses.