Back to the original posters question:
Drilling out the discharge holes will NOT give a larger pump shot, simply a quicker shot with less duration, with the possible result of a delayed hesitation.
The pump shot may be increased by increasing the pump cylinder volume. Increasing the pump cylinder volume may be accomplished by:
(1) Changing the height of the pump cylinder by: (A) using a shorter pump or (B) shortening the effective length of the pump rod or (C) changing the radius of the relation of the pump rod to the intermediate pump arm.
(2) Changing the diameter of the pump cylinder (more difficult than A above) by boring the pump well oversize, and fitting a custom made oversize pump.
Reiterating, the pump cylinder volume determines the pump shot volume; whereas the discharges nozzle orifices determine the length of time for the pump shot to be delivered.
As to the feed versus slot discussion: sometimes engineers are asked to resign a product so that the product will still work although less reliably at a lower initial cost. In the manufacture of a carburetor bowl, much less expensive to cast in a slot rather than machine a seat, a hole, and a cross passage after the casting step.
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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