Cliff doesn’t rebuild carbs anymore, he retired building. He does sell parts.
Before doing anything, buy cliffs book. He describes a procedure for verifying the needle/seat actually seals, and if it doesn’t how to fix it. If the needle has a slight leak, it’s possible the float bowl can slowly drain back thru the pump.
Lastly, the first design of the Q-Jet did suffer from main well plugs leaking. The first design plugs look just like tiny freeze plugs, almost everyone of them leaked. Rochester redesigned the plugs in 71 (I think) it’s a much better setup. The new design is basically a solid aluminum slug that’s driven into the hole, and then peened over the main body. The new design RARELY leaks, but still gets blamed. The myth refuses to die!!
It’s easy enough to check for main well leaks. Remove the carb from the engine. Use a couple 2x4s to elevate the carb above your work bench. Use a scrap piece of fuel line bent at a 90* angle, thread it into the fuel filter housing. Tighten the line so the bent end is above the carb. Carefully fill the float bowl thru the vent. Put a piece of clean white paper under the carb, and let it sit a few hours.
If the paper is clean and dry with no indication of fuel, the well plugs aren’t the issue.