From reading about the A bomb sorties I ahd the impression there was rather more involved in the bomb bay attachments and connections than for a conventical weapon and a lot of mods had to be made to carry the nukes. Of course the b29 was awhole genration ahead of the Lancaster in terms of design and performance and by the middle of 1945 the Lanc must have looked very dated alongside the B29 even if could still do a good job in Europe having done much to wreck the Germans remaining air defence and aircraft and weapons production capabilities in previous years