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It is an intriguing idea. I'm stepping way out of my already limited knowledge here but it would seem that weight would be the deciding factor. That is either it can lift the payload or it can't. Other hurdles would be easier to address I believe.
As far as the Lancaster actually being considered for this task when I read one of the other posters mention that in the other thread that was the first I had ever heard of it but I did for sure find that interesting.
The main deficiencies of the Lancaster were its range, altitude and speed.
The Lancaster could not have dropped the bombs from the base used by the USAAF for the missions. But there were closer options had the need arised, such as Okinawa.
LancTest Beds
A couple of pictures of saddle tank trial Lancasters on this page. I believe they were designed for operations in the far east.
Where does that get our 2,400 mile Lancaster trip? Japan still seems to still be in range.
Tropical SummerFS gear - 2450 rpm - 4.7 boost - 209 mph - 222 gal/hr - specific air range 0.94 ampg
2,400 miles was done at 68,500 lb (12,000 lb Tallboy). With more fuel available with 72,000 lb I think there's plenty of room for some higher throttle/rpm flying.