Nice job on the wheels, Bernard (@lis). You are right, the Doolittle B-25s did not have a regular bombsight. They came in at tree top height to avoid Japanese radar and other detection devices, so the normal bombsight wouldn't work. They made a manual sight to replace the regular bombsight. Not taking the regular gunsight also saved a lot of weight. They also removed the belly turret to save weight, along with a bunch of ammo. They put two painted broomsticks in the tail to hopefully scare Japanese fighters away.
Here is some info from the Wikipedia article on the B-25Bs that were used:
"Initial planning called for 20 aircraft to fly the mission,[20] and 24 of the group's B-25B Mitchell bombers were diverted to the Mid-Continent Airlines modification center in Minneapolis, Minnesota. With support provided by two senior airline managers, Wold-Chamberlain Field's maintenance hangar was the first modification center to become operational. From nearby Fort Snelling, the 710th Military Police Battalion provided tight security around this hangar. B-25B aircraft modifications included the following:
Removal of the lower gun turret.
Installation of de-icers and anti-icers.
Mounting of steel blast plates on the fuselage around the upper turret.
Removal of the liaison radio set to save weight.
Installation of a 160-gallon collapsible neoprene auxiliary fuel tank, fixed to the top of the bomb bay, and installation of support mounts for additional fuel cells in the bomb bay, crawlway, and lower turret area, to increase fuel capacity from 646 to 1,141 U.S. gallons (538 to 950 imperial gallons, or 2,445 to 4,319 L).
Installation of mock gun barrels in the tail cone.
Replacement of the Norden bombsight with a makeshift aiming sight devised by pilot Capt. C. Ross Greening that was dubbed the "Mark Twain". The materials for this bombsight cost only 20 cents.[18]
Two bombers also had cameras mounted to record the results of the bombing."
