Being the block is at the shop maybe have them sonic map it for thickness. This way you'll be able to see any coreshift and actual thickness around the cyl wall. This will also let you know how much room there is for future overbore if needed. The 406 was also used as a test mule for the 427 development. Just as the 390hp was for the 406. This was a interesting time in Ford production as their performance years were gearing up.