TH350 Decoding Question

[glord]

I’m in the process of verifying the originality of the drivelines in my ‘72 K10 and ‘72 Blazer 4WD. I’ve found the Engine Codes and Differential Codes, but I’ve not been able to find the Transmission Codes. Both have TH350s. Nothing on the right side of the housing just above the pan, or on the boss behind the bellhousing flange on the passenger side of the transmission. Nothing on the Accumulator Cover. I did find Y2D07N and YZM10N (possibly Y2M10N) stamped on the right side of the transmission pans on the K10 and Blazer respectively, however I’ve not seen any reference to what these might be.

I see reference on line to an ID plate that was attached to the tail shaft but not the case on either truck.

Any advice as to other locations I might check? Apologies if this question has already been asked and answered on the forum. If it has I’ve yet to find it.

Thank you.