Will leave the Holley bogging to others, but for the gaskets/spacer:
(1) Remove the carb, gaskets, and spacer.
(2) Place one of the gaskets on the top of the intake, line up the mounting bolts, and check for leaks. You need at least 1/8 inch (3/16 is better) gasket to intake mating surface all the way around.
(3) Check the gasket(s) to spacer in like manner.
(4) After draining the fuel, turn the carb upside down. Look for any passages OUTSIDE the area covered by the spacer (idle screws, vacuum passage to PCV, or distributor, or???). If you find any, check that the gasket is either cut out (to vacuum, if necessary) or covers these passages.
There are literally 100's of mounting gaskets. You have to make sure what you have seals.
A four hole under the carb would not help.
Jon.
__________________
"Good carburetion is fuelish hot air". 
"The most expensive carburetor is the wrong one given to you by your neighbor".
If you truly believe that "one size fits all" try walking a mile in your spouse's shoes!
Owner of The Carburetor Shop, LLC (of Missouri).
Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings.
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