Rocker Arm ID
 

I started to disassemble a 440 engine today and noticed that the rocker arms on the left and right heads are different. The rockers on the right are stamped T79, T711 & T712. The rockers on the left are stamped TH-2 and TH-5. Is there a list that shows what each of these rockers numbers mean any why they may have been installed on this engine like this? There were different head gaskets on the heads too.