Early in the Manhattan Project, the B-29 was having some developmental issues, and there were some proposals to use Lancasters as an alternative. The RAF dedicated a unit of all black Lancasters to start training and troubleshooting the challenges involved. One issue was range, and the British actually pioneered some in flight refueling practices to make a workable solution. Senior American personnel strongly objected insisting an American bomb be dropped by an American bomber, and they concept was dropped once they bugs with the Superfortress were resolved.
....interesting post...! a bit of aviation history....if I remember correctly, the United State Army Air Forces (yes, with an “s”) never did completely fix the engine fire problems on that great aircraft...I seem to remember reading some years ago that engine fires were always a concern to B-29 crews....
https://www.youtube.com/watch?v=5XX9ptCNpik
Thank goodness for Mark Felton, he is a treasure trove of WWII history.
The back-up plan was the B-32. Built by Consolidated - think of a B-24 with a conventional tail. The "Dominator" was not produced in large numbers.
The ultimate success of the B-29 can be seen in it many roles and being extended into B-50s, ... etc.
I remember seeing a picture of a Lancaster taking off with one of those huge bombs. Its wings curved upwards.