340 question?

So I scored a 70 a body 340 today (200 bucks). Its standard bore but the crank is turned 20/20. Any idea why a standard bore 340(w/ original pistons, oil pan, dipstick, balancer, etc) would have a crank turned that much? Also, it looks like the crank will polish, but what is the most you can turn a steel 340 crank? Thanks guys.