Raer Drum Brakes

[GMC Jim]

Installed new brake shoes and wheel cylinders on rear of '71 rear wheel drive pickup. Drums are slighly different!! Left drum has casting no.- 3982297; Max Dia 11.09 and is 3 5/8 depth.

Right drum has casting no.- 3989541; Max dia 11.09 and is 3 7/8 depth. Note there is a difference of 1/4" in depth !!

I called the local GMC dealer; parts dept. and was told the drums were discontinued and the last part number on reference was 3984855. !!!!

As the left drum is badly scored , I desire to replace it... but my question is :- what is the right drum to use and does the 1/4 depth difference matter...( I would think it would !) The depth measurement I am refering to is the maximum outside measurement.

Also is there a range of barke drums that are interchangable. example '70 thru '79, maybe... Any help is sure appreciated......Jim