Holley stumble trouble

^^^^This is what I’ve suspected the whole time. Question is, how to correct it? I’m not sure I’m interested in trying to drill out these tiny holes or press in new ones. Perhaps a replacement adjustable metering block is in order here. I briefly considered a ProForm main body but they do not come with blocks and there is no provision for a vacuum advance port if using my existing block.

Negative. It’s the primary. I’m gonna measure again to be sure but I was pretty careful the first time around.
I would drill the Primary MAB to .026, the IAB to .067, and the IFR to .033
Here's a good read for modifying and tuning. It's not rocket science, but is time consuming. You will also have a lot of folks looking at your tail lights.
Carb Tunning