What disc backing plates do I have

[gmc4x4can]

Im doing a drum to disc on my 70 k10 with the disc parts that the previous owner gave to me with the truck. Ive ran into a problem. The disc rubs on the backing plate at the top of the pic. Ive pointed to the stamped in hump which is near both caliper ends, I cut out these humps but now i find that the offset of the mount is different and i cant even get the inboard pad between the plate and disc. The bottom plate works fine, no hump and disc doesnt rub, pad and calipers fit fine. They are 1/2 discs. I would like to buy another like the bottom one, but need to know the year I guess as I didn't buy it. Thanks guys
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