The numbers on the lugs are simply a serial number-the number is read 'two digit' then 'three digit' -the two digit being the batch number, and the three digit number the individual number within that batch. There is NO way of dating the engine from the serial number=other than in a purely sequential fashion....ie a higher batch or individual engine number was manufactured later than a lower one...

Your engine is missing quite a lot of carburettor parts.....

ChrisM
'ffkiwi'