I was excited to see this listing, until I looked at the information and photos for it. Clearly it is a late 650ss bike from around 1966 or 1967, you can count nine fins on the cylinder too.

An original 61' 88ss would be green and dove grey, would have the fuel cap offset to the left and the speedo in the headlight bucket, and would also have a through bolt for the frame crossmember above the swingarm pivot as obvious visual clues among many others.

Hopefully whoever buys this bike will be looking for and know this is a 650, not the much rarer 88ss......

Benjyboy is talking about this:

http://cgi.ebay.com/ebaymotors/Vintage-British-1961-Norton-88SS-/290554033894?pt=US_motorcycles&hash=item43a65eb6e6#v4-37

hi beng,you are spot on i had one of the first 88ss green and dove grey 61 model,twin carbs but not on the later downdraft head ,great bike wish i still had it

Thanks for the info, I saw it on ebay and wondered about it.