Scufty, it's likely a 'service block', 1968 or later. Those did not come with CAEX type casting numbers. There is a series of number, letters and dashs\dots located around the
oil filter area of the block. Some help here guys, I forget the exact location. The numbers are small and hard to read as well as difficult to interpret without help (which you should find in abundance around here)!
Most likely being a 'service block' it also 'drilled' to accept hydraulic lifters. The original side oilers (first generation) accepted ONLY solid lifters.