I know a few people have tried various back brakes, but I'm sticking this here to show how, I'm going about it.
I'm using a set of MK2 Golf GTi rear brakes, the later cars have different calipers but I believe they would work.
I've had them squirreled away now for a while, as I took them when I saw them in the scrapyard.
Cleaned and painted, replace one bleed nipple.
First the difference between standard Mini flanges and Metro "Vented" flanges, I refused to pay the Turbo premium, as they are the same part. These from Rimmer Bros
A few minutes to remove the extra lugs and we are good to go.
Quick measure to show difference in size.
And Metro flange
Quick Maths 34.65 - 25.98 = 8.67 mm of difference not the 20mm I've seen said online
I also use a less that scientific method of measuring between the rear of the disc and the "steering arm"
Mini = 18.75mm
Metro = 27.60 mm
27.6 - 18.75 = 8.85mm, this is without the hub nut torqued up so 0.18mm of give.
So once the Metro flange is on, you have a small gap where the Golf brake carrier will fit.
Next step is to machine up a spacer and move the hole in and drill them 10mm to fit the new bolts.
For reference the Golf uses M10 x 1.25 or M10 fine bolts on the carrier.