mystery block

[cws10190]

so i have a block that i cant identify. it has a 4.134 bore no casting marks, and i can fit a 1/4 drill bit between jackets. this leads me to believe i have a .080 punched 390 that is not suited for 11 to 1 compression. its a four bolt motor mount has a 1u crank, c2ae-b rods trw l2245 std pistons. sonic checking is over an hour away at watson ruple performance, and my truck has no motor so i cant take it there. what should i do. does this sound like a problem?

[jayb]

I would venture to guess that you are correct about it being a 390 block bored to 428 size.  Have you looked into the water jacket to see if you can see "428" cast in there at the bottom?  You should be able to look down with a flashlight through the frostplug holes and see that in one of the holes if it really is a 428. 

If there is no core shift in the block it could still be used, but with the 1/4" drill bit fitting between the jugs this means that the wall thickness between the cylinders is at best .125" per side, so if you have a .050" core shift you could have one side at .075" and the other at .175".  No way to tell for sure without sonic checking it.  If it were me, I'd consider a sonic check mandatory on that block before I thought about using it...