This info is taken from a post on oldgmctrucks.com forums.
Somewhere on the block casting there will be what looks like a tag attached with slot head screws. This is actually cast into the block. (The actual tag was screwed into the wooden mold the block was cast from.) This will have a letter and some numbers.
The first digit is always a letter of the alphabet A-L. A=January,
B=February, C=March etc, etc all the way to L=December.
The next digit is a number 1-31 which is the day of the month.
The last digit is always a single number and represents the year of the casting.
Example: if the last digit is a 2, this could mean 1942, 1952 or 1962. To determine which you need the casting number and the Inliners International casting number chart.
According to that chart, casting number 2135412 was used on 270's from '46-54. Casting numbers 2324003 and 2404929 were used from '55-63.
Using that data you should be able to date your 270. However there were military 270s prior to '46 that Inliners doesn't list a casting number for. If your casting number is different from one of the above you may have one of these. The little tag code should still apply to it though.
