Never did like the Free Spirits use of 'free engineering' but I digress, I imagine a not good high pitched whiney noise. You know.... like 34:19.
SPHDonline here in that states has them for $200 In God We Trusts, so way cheaper than 270pounds (thats $335 Americans) but I don't know how shipping shakes out, or if they will. Keep looking farther than your local HD dealer, they're out there.
https://st-paul-harley-davidson-buel...most-xb-models
Just wondered whether the ribbed shiny outer skin of the belt is compatible with the Buell XB Pulley tensioner system ?
Should be. The Harley Davidson XR1200 drive belt has the same "ribbed shiny outer skin" that you're describing and uses a belt drive tensioner with exactly the same silica nitride pulley coating as the Buell XB series and completely compatible.