splitting the caliper body is unnecessary unless the seals are leaking, which they might after a petrol cleaning...:o, I would use a scotch brite and a strong detergent (Truckwash?) in hot soapy water and/ or brake cleaner.
The only issue you will have is obtaining the correct gallery seals, there are a few different types.
The bores of the caliper body aren't really critical, the piston should freely float on the seals and not be scraping the bore anyway.
As long as there aren't any flaky rusty bits in there (I'd be very worried if there WAS) then just give them a good clean.
Brake cleaner and compressed air are your best friends, along with a clean environment and rags.
JC

