That's fascinating - I didn't know of all those 3d trials. Does illustration 5 show a brass or silver 3d? If silver, the thrift plant was ditched in favour of the 'ring pull' design which can be seen on the proofs (the 6d had the same motif).
It's quite telling the pressure on the Mint designers - even after continuing with the GeoV coins dated 1936, they still seem to have been forced by deadlines to recycle many of the Edward designs for Geo VI - the bronze, florin and shillings; and even the halfcrown was only modified.