The numbers are actually the clock numbers for the sheet metal worker who made those individual parts.
Until early 1990's, the tin bashers were on piece rate so as soon as they had finished each part they would stamp their number into it and it would be tallied up at the end of the week to calculate their pay/bonuses.
Steve Barnes at VSM was able to tell me who made the bulkhead and inner wings on my 1971 4/4
Arwyn
