Richard I calculate it to be C4589683. But according to Rik's observations 422 of that first 1500 for the RAOC might have gone to the RAF, but I doubt anyone will ever know. Ron
These early Ariel contracts are difficult and any with RAOC / RASC splits are poorly documented. It looks to me as if the RAOC deliveries did not occur until after the RAF diversions....so my best guess is that they were from the RASC allocations and weren't sent to Ashchurch as originally ordered. The RAOC were something of sticklers for numbers matching serials...
The RAOC machines were probably XG 22001 - 23500...meaning that any lower numbers were RASC or RAF....If RASC then the serial was from the C1038302 - 1039801 range.
By chance, an image of one appeared on Facebook today.