Just update the history to show: 1970 K20 350 with a two bolt main. It threw a rod through the side of the block at under 80k. So what, plentiful and cheap to replace, even when I did this particular truck way back in the 80s.
My expectation on any engine in these old vehicles is... the lowest common denominator. Anything else is a plus.
OP should not pull his pack and upgrade anything if it's running fine. I can't figure for the life of me why you care what crank it has, especially if a crate is being considered. Unless what crank you have is a deciding factor to keep your engine and work it.
I think he should look at the crank and let us know.
This thread has been an interesting read; a lot of fun engine trivia stuff.
For the OP. I tend to work with what I got. If I want something specific in an engine, I go buy it. Rule of thumb... assume nothing!
You've read the prose here. What crank do you have? Exactly!