Hi Lorry. Welcome to the forum. It is quite safe here now that Julius and Brutus are gone.

The scooter wheels look good and should work well but the fit up gets complicated, they are probably too heavy and the larger diameter will put you out of the "mini rule" for competition.
Further, while the wheel is cheap, the hub is not.
Straight up I recommend the 8" plastic wheels you can get over there from a kite buggy shop. They are reasonably priced and are what Seagull use on their smaller yachts.
I doubt you will source Fallshaws over there.
Click around the forum some more and you will find all the answers you need based on a whole lot of experience of other people.
Have a look at the stickys at the top of the page. Cheers Cisco.

P.S. Read this. Heap of links on the last page.
http://www.bfslyc.org.uk/landsailor/Microsoft%20Word%20-%20Edition%2062%20Autumn%202012.pdf