Read here. Kent has documented his 69 340 swinger disassembly very well:
what #s to paint stamp onto 71 cuda 8 3/4 ?
being that it’s also a 69 340 dart (swinger/GTS) these mark could apply to your car well.
Not sure if axle assembly came to the final assembly factory as an complete rear axle assembly from another plant. I believe it did, that’s why there’s a 3-digit ID code for them.
