[FFR428]

Most 406's were not crossbolted. Although some were cast with the crossbolt bosses. Yes it's easy to spot and ID a original 62.5-63.5 406 block. Those are some of the few casting numbers that actually match up. Also you'll find a "HP" cast on the side and back of the block. Also in the lifter valley and by the cam journals inside. Most 427's have crossbolted mains. But there are a few industrial versions that were not crossbolted. That makes we wonder if this is a underbored 427 topoiler block (sold as a 406 sevice block) or just a thicker walled 390 punched out to 4.13. Pics of the block would certainly help explain what it is.