Here are a few possibles. It appears to be the odd size bearing for the Burman CP box. According to this website:http://www.petersclassicbikeparts.nl/co ... ARBOX.html
an alternative number for W6653 is N1540
and here on Ebay are alternative numbers:http://www.ebay.com/itm/AJS-matchless-B ... 2838369b02
Drags do the mainshaft bearing 3095-33 for the CP box...£40 https://www.draganfly.co.uk/index.php/a ... duct/5855-
John Budgen lists the N1540 at £32 http://www.johnbudgenmotorcycles.co.uk/gearbox.htm
Obviously check it is the right one...I should think a phonecall to Drags or John would confirm.
Edit...Or as Dave says below Ariel Club Gearbox spares list 3095-33 at £28.50.....sorry forgot that list. The list is dated 2012 so don't know if stock levels are correct to date? anyone know.