I was able to obtain from the UK's National Archives the declassified version of the file about the test drops of Royal Enfield Flying Fleas conducted in March-May 1944. I have asked for permission to reproduce it in its entirety, but do not have it yet. In the meantime here go some tasty morsels from it.
The "range of investigation" included the design of suitable crating, determination of the various bomb positions at which the crated bike could be carried, attachment of the parachute, the dropping technique and a suitable locating device.
The conclusions indicate the crated motor cycle can be dropped successfully from the bomb racks of the Halifax, Albermarle and Lancaster and from the paratrooper aperture of the Stirling IV. It should not be released simultaneously with a man (!) or crate. (It was suggested to wait 0.5s until after the drop for men to start jumping). When dropped from the bomb racks of the Dakota the aircraft cannot be flown at more than 110 mph. Also on the Dakota, it is difficult to drop the motorcycle through the door and is not recommended, the slipstream tended to jam it in the door even with three men pushing (!).
The crate evolved during the tests: the cross section of the main centre tubes was increased, an extra bottom longitudinal member was added. Modified wheel cradles were fitted, frame supports repositioned, front tubular guards to protect the handlebars were added and a rear tubular guard to protect the rear wheel. A wire parachute stowage basket was introduced. The weight of the motorcycle was 126lb and that of the crate 91lb.
I think this is the first picture I have ever seen of the cradle open,
Here is a picture of the bike attached to the bomb drop of a Dakota,
and here some details of the parachute release mechanism,
and this one shows the "lighting baffle" which was used for locating the bike after the drop,