Black estate was recently, but prior to my buying it, fitted with solid rear calipers of the 40mm variety...
I acquired a couple of pairs of used vented rear calipers with a view to sprucing them up... but on wire brushing all the crud off, the inner faces where the pads sit disintegrated in a pile of rust

So I am faced with buying two new calipers... All german were showing both sides yesterday at £72 each, but now only show one side

Then a thought occured to me... apart from the 2mm difference in piston diameter, the only remaining difference is that the vented calipers have an 8mm filler piece between the caliper halves...
My thinking is to split my two near new 40mm calipers and fit the filler pieces from the old 42mm calipers and reassemble using the longer bolts from the 42mm ones...
This raises three questions...
1. Is this feasible?
2. Is there a gasket between the parts, or is it a question of simply bolting back up? What sealant might be suitable?
3. What torque for the caliper bolts?