318 race engine 4104230-318 any info. on these engines?

The "X" block DID NOT use the same casting as the 318, at least not internally. They had much thicker cylinder walls, deck surfaces and main webs. The outward dimensions of the casting may have used a production 318 pattern and mold (hence the 318 part number cast into the side), but the inner molds and cores were different. They were also machined on 318 tooling with the smaller journals and a 3.91" rough bore. Like the T/A blocks, the main webs were thick enough to allow for 4-bolt mains, but the outer bolts may not have been drilled.

The lack of a VIN number stamped on the pan rail would indicate a replacement block, but this does not guarantee its an "X" block.