As an update - I have now cleaned, scrubbed and cleaned again the calipers. They are now painted (but not baked, this can happen on the car over time).
I've also taken the opportunity to paint the rear brake drums whilst the wheels were all off for new tires today. They are now refitted with new bolts.
The new pistons should arrive next week so can be fitted with new seals etc. and can then be refitted.
I have now also moved my number plate to the left hand side of the car (looks neat, but not symmetrical) so that the air scoop can work to its maximum. Whilst I was under the car I fitted a rubber air dam. When I get the brakes back on I hope this will lower the running temperatures in the WA summer!