Ok, let's be realistic - Your attempts to justify the Lancaster for the atomic missions is almost admirable if it weren't for the intrusion into the realm of the fantastic.
Kokura is just a bit south of Hiroshima, Nagasaki is south-west of Kokura.
We've been for the most part, discussing the magic Lancaster's journey retracing Bockscar's mission but yes, Hiroshima was further north - which would have also required a considerable amount of fuel to make the run from Tinian to Tinian.
And nice try, but my last sentence did not, in fact imply that. If one happened to read the rest of my post (reading comprehension helps a great deal, by the way) I stated that it would require quite a few of the Unicorn Lancasters to match the requirements if the 509th, which used interchangeable aircraft that could either carry the bomb or carry the nessecary instruments (weather or data).
Maybe I'll start a thread about the Stirling as a candidate for an Atomic bomber, should be fun.
Again, a Tinian-target-Tinian mission plan isn't required and Bockscar proved that. Tinian-Target-Okinawa is well inside the Lancaster's capability.
I think it a reasonable assumption that at least a whole squadron of "Silverplate" Lancasters will be available (at about the same cost as three B-29s), but there's no reason that these have to fly the weather/recon missions as well, although they could.
Short Stirling:
"The Stirling had a shallow bomb-bay 12.8 meters (42 feet) long, divided into three parallel "cells", each only 48.3 centimeters (19 inches) -- which would prove a limitation as the war went on, since the Stirling would never be able to carry the oversized "high capacity" or "blockbuster" bombs; it couldn't handle general-purpose bombs bigger than 225 kilograms (500 pounds). Along with the main bombbay, there were bomb-bays in the wings inboard of the main engines, though drawings suggest they were generally used to accommodate long-range tanks. Maximum bomb load was an impressive 6,350 kilograms (14,000 pounds), but that load could only be hauled for a relatively short distance; for long-range missions, the typical bombload was a quarter of that weight, 1,590 kilograms (3,500 pounds)."
The Short Stirling
Ramsey picked the Lancaster for a reason.