Hi All
Great site!!! I just bought a very nice 1970 Z28 all original 22000 mile survivor. I have a question about the date code on the motor.
This is the correct block CTB but the date cast is M 83 this is the original motor for sure because the numbers on the pad match. All I can find out is GM did stamp some blocks with this code when they were doing a change or examination. Any help would really be great.
Thanks Very Much

You should post a picture(s) of the pad, the block casting number and block casting date. Alpha date coding should end with "L"...so "M" would seem very out of the ordinary.

I found this over at the Camaro Reseach Group site
"M"-Coded Blocks
There is one exception to this convention that has been observed: some blocks have been seen with "M" cast codes. Research by the Saginaw Metal Casting Operations of GM Powertrain Division has found that these "M" codes are not date codes, but actually a foundry code used to indentify parts that were made to evaluate a casting process change. After evaluating the parts, the blocks would either be destroyed or released into production. There is no way to determine the date an "M"-coded block was poured.