1958 car with a Powerglide transmission? Stamped by distributor: F630B
F = Flint, MI
6 = June
30 = 30th
B = for use in a Powerglide car (having hydraulic lifters)
Cast (date) above starter: CON8 F258
F = June
25 = 25th
8 = 1958
A minor update, the engine block casting number is more like:
CON 3 F258
I also grabbed the casting number off the cylinder head if that helps. It is:
B52 848 850 (the last 3 numbers appear below the first 6)