The details of Upkeep and its spin-off (excuse the pun) Highball were kept secret by the Brits until 1963.
Twenty-three production Lanc MkIII's were modified by AV Roe to a Vickers design. They had standard Merlin 28 engines.
The first modified airframe was ED765/G which went to the RAE on April 8th 1943, the second was ED825/G which was delivered to Boscombe Down later the same month.
Twenty one aircraft were delivered to 617 Squadron. The serials were ED817, ED864, ED865, ED886, ED887, ED906, ED909, ED910, ED912, ED915, ED918, ED921, ED924, ED925, ED927, ED929, ED932, ED933, ED934, ED936, and ED9375. The nineteen aircraft used in the raids were selected from these.
ED825 was also delivered to 617 (on May 16th) but not used on the raids.
Regards Dave