A friend of mine has given me a 239 to use. But I was checking the numbers and before the identifying marks of A13M there is a 64 in a circle. Is this some sort of mark to show it was rebuilt? And if so would that designate the year it was done or identify the mechanic or shop? Thanks

 

Try this website

http://flatheaddrag.com/birthday.html

If I'm reading the chart right I'd say April 13, 1950

If it's a factory rebuild it should have a tag indicating bearing sizes, who, when, etc. Usually when rebuilt they grind off the original build stamping - I'd guess the one you have is stock or done locally if rebuilt.
The 64 in the circle is probably just an inspector number - otherwise unknown.

 

You have the date on the block correct. I was curious about the 64 as this I haven't seen before. But I could have sworn I read something about this type of mark but can't remember, drain bamage from a mis-spent youth. I have a chance to pick up two more flatheads, one is possibly a merc. And thanks for the reply.