Usually the block is OK. I understand that drag racer teams purposely leave a new block out in the elements to age for a year (cast-iron relaxes or such), then final machine it. But entire slant engines are so cheap or free, no need to fool with it.
Machinist for 30 years here...I can say 100% for a fact that metal DOES indeed relax.....many parts set to the side for a week or more before final machining....before and after measurements verify metals will settle and relax....
