This can get confusing, so bear with me, I will try and wrap it all up in the end...
The correct casting number for the T/A heads is 3418915 as stated.
BUT the casting number is also correct for some 340-4 bbl applications, and some 360 applications clear into 1972.
The 3418915 head letters may be a j, U, O, or Z.
The T/A head were s the same casting as the others, they were just machined differently.
So, the ONLY way to truly know if they are T/A heads is to look for the offset pushrod holes for the intake valves.
Barry