Interesting collection of photos of the two experimental Mini prototypes built and used for testing from October 1957, most of which have appeared in the various Mini books over the years except for the worm's-eye view pre-front subframe photo which is rarely seen. They were nicknamed "Orange Boxes" disguised with Austin A35 grilles and mainly tested at night. The under bonnet/hood photos clearly show the 950cc A-Series engine mounted the opposite way round to later production Minis, reasons for the change were given as carburettor icing and weak A35 gearbox syncro problems. The changes required the addition of a third drop or idler gear and also changed the cooling fan from sucking air in, to pushing air out into the other front wheel arch more efficiently. The 950cc engine was also reduced to 850cc to keep top speed down relative to the early braking power available at the time!
Note the battery is also up front but was later moved to the boot/trunk.

 

NICE!

 

So would it be correct to presume that the Wolsley and Rileys reached back to ADO15 prototype as inspiration for their grilles?

 

You could well be right, never thought of that! Even the way the grille opens with the bonnet/hood is the same as Elf and Hornets.
I think it is time someone built a replica "Orange Box"............I asked the Mini's Draughtsman, the late Jack Daniels, what happened to them at a Mini Meeting a few years ago at BMH Gaydon, he was pretty sure they were both scrapped in the early 60's by BMC.

Jack Daniels Obituary