I have two 455 blocks and the small pad where the numbers are stamped are confusing me. One has 30M123456. The 3 would mean Olds and the 0 would mean 70, correct? What does the M mean? The other has 30X123456. Same question, what does the X designate? The M block came out of a 70 442 Pace Car, the other came from ?

 

X is the Kansas City engine plant. My 1970 350 has the X.

 

M = Lansing

The remainder numbers are the last of the vin from the car witch it was in

 

Nope, sorry. By federal law, the VIN derivative MUST match the VIN of the car that the engine was installed in at the factory. The "X" represents the Fairfax, KS assembly plant. The Fairfax plant only built full size cars, so any engine with an "X" for the assembly plant was originally installed in a full size Olds.

 

The 30M block came out of a 70 442 Pace Car Convert. So Lansing would be correct for this block.

 

The M123456 on the engine should match the last part of the VIN. If it does it's the engine that was originally installed in the car.