[rotorwrench]

I've seen three digit date codes mean a number of different things. Tires used to use a 3-digit code but with the last digit being the last number of the year, there is no account of what decade it may be. A lot of times a code for the week of the year is used (52 in all) and sometimes it is the biweek of the year (26 in all). Three digit codes for tires gave way to 4-digit codes on tires in the year 2000.

If the code for that engine rebuild is week and year then it could have been around end of July of 1941 or 1951 but it's hard to say so many decades since. It may have been late July of 1931 but it wouldn't even have been a year old yet by that time.