Why don't you use a carb gasket like this? It is 5/16" thick so it is a good heat insulator, and has "spacers" in the holes to keep the clamp load solid and not warp/break the ears off of your base plate of the carburetor. It also keeps the dual plane split all the way to the carburetor so the throttle response is not compromised on a "true dual plane" application:
BASE GASKET
PART #: 108-18
Features
Fit Holley Model 4010, Model 4150 and Model 4160
1 3/4" Throttle Bore
5/16" Thick
http://www.holley.com/108-18.asp
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