[Excaliber]

But not all SO's had cast numbers!

Screw in feeze plugs on the side oiler. BUTT, just because it DOES have screw in freez plugs doesn't 100% mean it's a side oiler. Some SO blocks were cast that way, but never DRILLED that way and were destined to become industrial blocks.

Then you have the service blocks, cast to replace broken or worn standard issue "auto" blocks. These generally have no casting numbers.

One thing for sure, it DON'T got screw in freeze plugs and three bolts per side for cross bolted mains, it dang sure aint no side oiler.

...could be a 390 for that matter!