Need big block help

Lefty71 said
The "M" does indeed mean that it's an aftermarket Mopar block.
Why do you think it was cast in '71???

I thought it was 71 because I found 12-6-1 cast on the block. After reading the Mega Block write up I'm sure that's what the block is and it is a 2001 cast. Going to look later and I hope I don't find MOPAR over the numbers.