I'm not sure what they are calling a 'brake backing plate' - although it does bring to my mind the back plate of a drum brake.

You are somewhat limited in where you can place the caliper. It needs to be more or less vertical so the bubbles will rise to a bleeder valve. And there are suspension pivots and steering arms. You could swap them left to right if you put them in front of the disc instead of behind. But I think you will interfere with the steering mechanism or the sway bar there. Maybe in the 11 o'clock position (looking at the left front wheel)? I seem to recall trying some different positions with mine while I had everything apart and coming to the realization that the behind-the wheel 3 o'clock position was the best (that's what the factory rally cars used AFAIK). If you have a caliper mount you will need to redrill it anyhow to fit the 544 spindle - it wouldn't be any more work to use a different positioning. Well - not much more - I reused one hole and had to redrill 3 of them.

I cut and rewelded my lower shock mounts at a slight angle to retain the full turning capability. I'd say that about 1/2 of my time was spent fighting with stuck rusty shock mounts.
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I'm JohnMc, and I approved this message.