No such thing as thicker or thinner. In any B or RB. The cold climate 400 "230" blocks are a thicker block because of the propensity to freeze crack in bitter cold. Those generally have thicker cylinder walls. Everythign else is a cr_p shoot. If you are really worried, or exceeding (realistically) 550hp or increasing stroke beyond 3.75, then have the block sonic tested by someone who knows how to use it. Then you'll know.