Looking at the first pic, it looks as though the top center hole for the bell housing is tapped. Newer blocks don't have that provision. That would put that engine in the late 50's to 60's era. 283/327/350
There may be a vent fitting next to the distributor on the driver side. If so, that will "somewhat" date the engine too. (vented block - small journal crank) 283/327
Just trying to get you in the ball park.
But in the end, the casting #'s will tell the tale.