A lot of Tallboy & Grand Slam steel bomb casings were manufactured in the USA in 1944/45 for supply to Britain. They received their explosive filling in Britain.
US designation for Tallboy - Bomb, 12,000lb GP T10
US designation for Grand Slam - Bomb, 22,000lb GP, T14
In Feb 1945 a single B-29 was taken from the production line and modified to carry Tallboy. This involved remodelling the two bomb bays into one and modifying bulkheads to accomodate the weapons as well as fitting a new set of one piece bomb bay doors that would partially enclose the bomb. A lot of the design work on the modified bomb bay had already been done for the dropping trials with the "Thin Man" atomic bomb dummies. This aircraft was used for test drops between March & June 1945 at Eglin AAFB in Florida, following which a report was produced that recommended that sufficient B-29 aircraft be converted to equip one bomb group that would specialise in dropping these weapons.
The RAF Special Missions Wing, comprised of 617 & 9 squadrons, were being readied to deploy to Okinawa in time for Operation Olympic, when the war ended. The plan was for them to be in position on Okinawa by 15th Oct 1945. These squadrons had been specially requested by the USAAF and were to be the first aircraft for the RAF Tiger Force to deploy.
Then came Project Ruby in 1946 and also Project Harken. A report on the latter can be found here
https://apps.dtic.mil/sti/tr/pdf/AD0080379.pdf
A US development was the Tarzon bomb that was used in a very limited way by a single USAF bomb group in Korea.
https://en.m.wikipedia.org/wiki/ASM-A-1_Tarzon