You sure that's a 153 tooth flywheel? 153 (little) and 168 (big) are the two usual sizes but GM did do some oddballs from time to time.
Almost all GM blocks are drilled/tapped for both bolt pattern starters- straight and staggered. The fact you have an older block doesn't mean it is any different in that area than the more modern ones. At least back to the early 70s (don't know about stuff built in the really early days). Some may not be dual bolt patterned (only one or the other) but that doesn't mean the starter pad is in a different location.
Also see my reply to your post (and others) in the other thread.