If you block the passage and keep the heat riser valve and it shuts closed as it should - where does the exhaust from the passenger side go?
My 2cents - Put a heat riser spacer in there like they used on FI cars that eliminates the flapper. You can then block the passage holes.
Aluminum intakes can run well without the exhaust riser heat but cast iron will take a LONG time to heat up.
On my 302 I have the FI spacer that eliminates the valve function and the aluminum intake with only the drivers side manifold passage blocked. The choke stove on the manifold still gets enough heat to work. and the car warms up fast. I needed to block one side just because the heat was getting to be too much on the carb for todays gas. New fuel seems to percolate much more than the good old stuff did.
-Mark.