so whats the conclusion lots of input, i know several t/a aar folks and have one myself, and we have mixed bag,this may be a little premature but it seems that blocks made in 70 have this T in 69 no T. QUESTION IS WHY?? like one person on this forum suggested, easier to indentify?? means track? not sure, but i have a call into another source that worked at chrysler, untill then we need to keep digging, this is very interesting.. BARRY i know youre working on this, please post update on youre thoughts....