I've been following your thread for awhile as I also did my first carb rebuild on my 74 Carter BBD last fall. The adjustments were all off; float setting, meter rods, choke plate etc. about the only good thing was that my pump spring seems fine. The rebuild kit I used didn't supply one, and i got 10 years of farm dirt out it. But after the rebuild I also got "the stumble" during acceleration, especially when its cold out.
The reason I bring this up is that my friends car, 74 dart custom with a /6 1barrel had a stumble also, but after replacing the gas tank and associated vacuum lines last summer it runs perfectly, warm or cold weather and when you open the gas tank you can hear that hiss of pressure equalizing.
This leads me to think that you "may" want to check for air leaks in the fuel lines while your poking around. It certainly can't hurt. How this ties in with the fuel pump and fuel delivery under load is still something I am learning being a newbie myself.
Hope it helps some.