[mrennie]

The 73 block has a tad thicker cylinder walls then the 70, that’s one of the reasons for the changed part number as they knew catalytic converters where coming and the motors would run hotter.

Without doing a sonic check, you will never know if one block has thicker walls than another, where it counts.

I checked a 71 and 73 block I had, both very different castings, and the 73 had core shift and the entire passenger bank was the thinnest, on the thrust side. From a visual inspection, all other items looked good (lifter bores, frost plug holes) and I would not have suspected thin bores.