I agree with the rebuild sentiment, then you know it's done properly and the brake will feel light but firm. It's an easy job - I use a releasing agent then clamp each piston back and use the airline to move the pistons individually before disassembly. I've never had a problem - if you get a stubborn one then I have a spare master cylinder rigged up with a short hose; I just pump the sticky piston out with the extra pressure.
The reason for my post is that I'm rebuilding an MC21 (with a Magtek front wheel) for a friend and he's supplied me with standard and CBR900 calipers. The obvious difference being that the 900 calipers are threaded in the mounting holes. This makes it fiddly to tighten them so I guess I'll get the threads drilled out - can you see any reason why this might be a problem?
Cheers, Paul