What if you take 40 500lb? 40x500=20000x3=60000lb
4x4000=16000x3=48000lb
48K would be more than sufficient if you hit. With 40 bombs it's even more difficult to get the required hits than with 4. IF you drop 40 bombs with minimum delay at 350mph, the resulting line of impact is almost 90 yards long. And you still have the problem that your drones are too far apart, so in the end only a tiny fraction of your bombs achive direct hits.
I'm not saying it's impossible to kill HQ with one set of B-29's only, but so far I had no success, not enough hits on target. Maybe I try again during the week.