I'm sure you heard me talk about Dave Shoe's drill bit test? Dave came up with a slick way to field test a block with drill bits to tell what size cyl wall cores it has. The cyl wall cores are behind the blocks 6 freeze plugs. Yep you need to knock one out on each side. This will expose the wall core area and you'll see the gaps. Std 406 wall cores will snugly fit a 13/64" drill bit shank. 428 wall cores a 8/64" bit shank. And check each side!! One of the 406 blocks I had was cast with std 406 cores on one side and 427 cores on the other!! Very werid and odd that could happen but it shows it did. This is just a simple way to see what wall cores are inside. A sonic map is the best way to tell overall thickness.

As far as the crossbolt bosses the block will have 3 nubs on each side opposite the end of the 3 center maincaps. Some 406's have them and some don't. It's nice if they are there as you can easily crossbolt the block with new maincaps. You can still crossbolt with out the bosses but there is a slick way to do it if they are and your using oem or aftermarket billet caps.

Value is a tough call. But my C3-D bare block and C2SE-C heads all exact same date code matching sold on epay for $3k. My 3x2 was original to the engine, matching carbs, polished intake and aircleaner sold for $1800. I've never seen these blocks and heads go that high before. Add $400 for your 428 crank, $150 if the rods are big bolt and $150 for the slugs. $200 if the rockers have the cast iron slotted rocker stands. $200 if the original balancer/pulley is still there. Oem dual point dizzy $150-200 and all the other odds and ends. So about $5k more or less?? The value will go up in time even more.

G.