In looking through my pile for a block for my back up race motor, I found a EDB block that a 1/4" drill bit will not fit between cylinders (freeze plug), I think I will take it apart and sonic check it, any other thick blocks out there? 

EDB block as per our conversation yesterday on the phone.
  
Do you know the exact thickness between the cylinders?  I ask because assuming the ¼” drill bit barely fits between the cylinders, the mathematically derived valve for the cylinder wall thickness for a standard bore block at that point comes to 0.190” which is already a slightly better than average value for thicknesses at that particular area.  That mathematically derived value assumes no core shift.  From all indications, your drill bit test points to the cylinder walls actually being thicker than that.  The sonic test then would collaborate this as the two sonic test values from the two cylinders at the same areas the drill bits were inserted and added together should add up to the mathematically derived value for both cylinder wall thicknesses.  The sonic test is still necessary if for no other reason than to see where the core shift resides.  I trust that made sense.
 
Some of the early 272 blocks had ‘very’ thick cylinder walls.  Have come across two of those and both sonic tested ‘very very thick’.  Took one of them and made a 4” bore out of it for the customer and that engine been running well for over thirteen years now.  It’s not a hot rod, just a cruiser with a 2V carb but runs fine without any heating issues.  The walls were thinner than I’d prefer for a performance engine but is running okay in its current application.  The other thick walled 272 block was treated to a 0.020” overbore back in 1991 as that’s all it needed to clean up the cylinders.  That engine had well over 100K miles and could have been a re-ring job but the engine was being restored to a ‘like new’ condition so it received a 0.020” overbore.  That 0.020” over engine is still running great today with a lot of miles and no issues other than oil leaking from some of the gaskets now.
 
With there being a documented 312 built by Ford Engineering in 1954, I’d not be surprised if some of those early thick walled blocks that were not used for developmental or testing purposes ended up in passenger cars.  There were a couple of runs of large bore lifter blocks that ended up in passenger cars being machined for the standard ½” shank lifters.  The first run of blocks slipped through the process so fast that the blocks were not caught in time to pull some of them out for development work.  Hence the second run of big lifter bore blocks.

Lorena, Texas (South of Waco)