If you have been hanging around smelling a lot of old gasoline and gathering up information on Cudas and Challengers you tend to know were a serial number would fit via your information you have collected. Sometimes the number is known via someone owning a car and asking about if you know of a motor or a body a motor came from. There are a few of these kinds of people doing this for years and it takes time to amass such information off sites and auctions, ebay on and on for years and years. I have been collecting since 1978 still do not have every 1971 Hemi E Body hardtop that was built. The 11-18-68 is the casting date and it went into a 1970 E Body and 11-11-68 usually is a 1971 Hemi Motor Build. First in first out was not used back in the day. I have seen a factory block stamped with .0015 on the Mains. When we rebuild the Hemi motor back many many years ago we had to use another crank that was 10 th. under because we could not find .0015 over size bearing and did not want to cut the hardness from the crank. Motor still running after 30+ years with that crank being changed and the original crank if the car ever get sold will go with it.