Hey everyone, Flandy here.  The reason for this post is a request for some help.  I've got a 68 coupe with a 427, casting # of 3916321 and I was trying to see the original serial.  Well, I got the number, and it is 18J159863 and according to my research, it should read T8######.  Soo, could this be a replacement serial number on the pad?  Thanks in advance for any info.  Also the numbers stamped into the pad are 1/4 or 5\16 is this the correct size?  Flandy

Hey everyone, Flandy here.  The reason for this post is a request for some help.  I've got a 68 coupe with a 427, casting # of 3916321 and I was trying to see the original serial.  Well, I got the number, and it is 18J159863 and according to my research, it should read T8######.  Soo, could this be a replacement serial number on the pad?  Thanks in advance for any info.  Also the numbers stamped into the pad are 1/4 or 5\16 is this the correct size?  Flandy

You have the correct casting # for a 68 427, but the S/N should start with a V for Flint or a T for Tonawonda e.g T0623MR Tonawanda 0n Feb 24 MR= 427/430 and the 19S711090 which is part of you VIN.

I can't find anything in my books with a 18J
 

Looking at the passenger side pad on from standing in front of the engine, the first numbers will be for the engine type.  All 427's were made in Tonawanda, and a 3916321 casting is an early 1968 427 block.  So the number should start with a T.  The next two numbers represent the month the engine was put together followed by two numbers which represent the day in the month.  Then there will be two letters which represent the horsepower.  IL = 390hp 4sp, IQ = 390hp auto, IM = 400 4sp, IO = 400hp auto, IR = 435hp 4sp, IU = 435hp 4sp with alum heads.  These numbers and letters are approx. 1/4 inch.  The set of numbers to the right are about 3/8 inch and represent the serial number of the car.  It starts out 18S419365 (just an example).  Also look on the passenger side of the block by a freeze plug.  Upside down will be a casting date.  This will tell you when the block was made.  A = January, B = February, etc.  It will be a letter, then date (day of month) and single digit for the year.  Hope this helps.  P.S.  give us the serial number posted on your windshield and I can tell you which month your car was built.  Then you can tell by the casting date if your engine block is correct for the car.

Mark
corvette42738431.7603472222