This is original information from Nortons stating all clearences and procedures.
All engines should be built to this specification and not deviated from, even though some clearences seem excesive they are correct,
i.e. if a closer cylinder bore clearence is used even a modern piston will seize.
The following Microsoft Word document contains 14 pages of original preperation for racing, kindly rewrote by Ian Allen (I.O.M) allowing you to read it all a little better than the previous scans of original copies!