Wemoto recommend Iridium plugs NGK IMR9A-9H trade price is £14.48 +vat.
Fowlers parts are IMR9C9HES - 5766 £27.35 inc

NGK own web site says IMR9C-9H 6777 ebay do for around £54 for 4.
cant buy trade as cheap as ebay.
so take your pick

obvious answer, take one out and see what is fitted...