I don't think you can buy new backing plates, I did my conversion a couple years ago and one side might of been available new, or neither one was, I forget. I ended up looking south for clean ones, the backing plates around here I'd find were typically rusted pretty good. Also can be a minor pain to pull in a yard, depending on how the yard is setup. I found mine on ebay, think the person was selling many sets over time for people converting to rear discs. Then found the calipers locally at a salvage yard.
383 CCC QJet- BRF 2004r-8.5" 3.42
350 MAF/SD TPI- CRF 2004r-7.5" 3.42
-81'Grand LeMans Safari Wagon
350 CCC Q-Jet/CZF 2004-r/8.5" 3.73
Stockish daily driver