I have had some contact with the race organiser for Sunday.
There will be entry on the day. The race limit is 500 but entries for the past two years have been just over 400 and we've never yet had to close entries so I'd predict you'll be OK. There is already a good number of Wilmslow entrants both by post and online.
Of course, if you want to be sure and collect numbers that's fine. Are you visiting the Illuminations?
Now theres a thought!!
Nick.