19170538
427/454 Bare Block 

• New casting incorporating the best designs of Mark IV and Gen VI
• Production type cast-iron 4-bolt block
• 4.250" finished bore
• 4.310" max bore (non-siamese bore)
• Machined fuel pump pad
• New water jackets for use with Mark IV or Gen VI heads
• Revised oiling to allow for bigger cam bearings/cam lift 
• Bolt boss (not machined) added near distributor hole like 8.1L
• Can be drilled for use with 10-bolt front timing cover
• Additional clearance added for roller timing chains
• Auxiliary oil pressure line added to front of block
• Racing style oil filter cast feature with added oil pressure port
• Additional boss for manual transmission clutch pivot (machined)
• Additional material added around lifter bosses