I would look at it this way...
start shopping for a crank.. look for the best deal.. and depending if its a large main or small main that would dictate which block you use..
yr back I had a 340 block I sold off to use the money to build a 385 cui class rule engine.
and planned on using a early 360 block.
as soon as I sold off the 340 block all I could find deals on for cranks was for 340 mains..
some killer deal on a k1 3.79 stroke crank came available but It was a 340 main..
I didn't have the 340 anymore so couldn't take advantage of the killer crank deal.
shop for a crank first ....that will dictate which block to use.
that's my