Porsche caliper swap help

I am trying to fit Volvo calipers to my Porsche 944 with a LS. The fronts bolt on perfect, but the rears not so much. To get Porsche replacements locally is impossible, and to rebuild them costs as much as new Volvo calipers, that won’t replace any of the hardware either.

The rears problem is the spacing of the holes. I have a few ideas, but the one that looks to be the easiest would be to have the backing plates milled down 1/4” and then use a piece of 1/4” steel to mount the caliper to the backing plate. I made a very rough sketch of what I am thinking.

I’ve also considered filling the original hole with weld and building up the mounting surface with weld. Having it milled and drilled and tapped to match the Volvo spacing. Any other suggestions or opinions would greatly be appreciated.

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