"is it also a 3 1/16?"
Yes, it is a 3 1/16. It was a standard block with no cracks that I bored out to 040 over. This is a post war replacement block. Ed
I have one of the same blocks you working on. I believe these were cast after ww2 as replace blocks for 221 ci. They were machined with a 3 1/16 bore. Mine had plenty of meat for a 3 3/16 rebore. Great block for a fresh 239 ci engine. hHave your machine shop check it out for wall thickness and go for it.
Hell yea, you say it ain't cracked, then it's got to be worth rebuilding. I would definitely get the bores sonic measured, this is because as I/we have now realized these small bore 59 blocks ain't all the same castings. As I stated mine has the pencil ledge, and looks like it may go 3 3/16", but not much more, these blocks were cast to be bored for the smaller bore. I have a couple of 21 stud blocks here and they look like they have thicker cylinder walls.
But, big but, yours has no ledge, so maybe it is a normal 59 type 3 3/16" casting that was only bored to 3 1/16". If this is the case it will go 3 5/16" and bigger, just as a regular 59 block.
You may very well have just scored a peachy block.
Martin.