The only true crossbolted 406 block I've seen has been a C2AE-BD block. It was rumored a NASCAR block back from the day. This was back in the late 70's. I've had both the C3-D and V blocks and both were cast with the crossbolt bosses but had 2 bolt maincaps from the factory. The maincaps were both C2AE caps and grey iron not nodular like the C3AE 427 caps. Anything is possible and it's not the first I've heard of owners finding crossbolts in their 406's. Have you checked the cyl wallcores to see if it has 427 cores? STD 406 cyl wallcores can fit a 13/64" drill bit shank between them. My C3-D block had one side cast with 427 wallcores and a 7/64" bit shank a snug fit. Weird but true and some do have 427 cyl walls. The 406 was a "tweener" engine. Developed from the 390HP and the precurser to the 427. The 406 is not only very rare but interesting as it was the test mule for the development of the 427. The only way to see if the block is an original crossbolt block is to measure the mains to see if they have been line bored. You need to line bore the block when you install new maincaps. This will tell you the real story. If the engine is built and running enjoy it till it needs a rebuild. Then you can get to the bottom of things. But if the engine is out and apart check those mains!!! Very cool engine and thanks for posting. The 406 is one of my favorite engines. Let us know what you find.


G.