SBC Casting # / Date Question

Hello all,

Can anyone tell me what if any significance this has:

T21 CONV 1

Found on right rear of block above bell housing flange on a 1969 350 chev. where the Casting Date should be

Hunter

 

try Mortec.com

 

I tried several web sites including mortec, no luck ......

Someone else have a suggestion?

Hunter

 

Maybe try www.chevytalk.org

 

Looks like this one is gonna stump everyone!