Just re-looking at the pictures, comparing George's and Pishta's manifolds... Pishta's, as he stated, is a '66-'69 version, George's is definitely post '70- it has the larger bypass fitting for the aluminum water pumps...
Now that is a good observation about the larger bypass fitting, post '70 for alumnium water pumps.
OK looking more and more like that is the original 2 bbl single plane for that 318 engine with the date code on the block of
7-6-70. Engine came out of a pickup with the truck oil pan on it when I got it.