Discovered a long list of M20 part numbers and descriptions, take a look.

http://www.docstoc.com/docs/76504745/Category-Description-Engine-Cylinder-barrel-Engine

email (option): sales@victorylibrary.com

Hi Panic,that looks like a breakdown of Russell Motors parts and price list,
if you google them the prices appear in the correct place.
Hope this helps
cheers Rick

email (option): richardholt@rocketmail.com

The down side of their BSA parts .pdf download is its not been updated since Oct 2006 so its not much use for prices ... last time I looked anyway.