Whats the difference between XJ550 and XJ750 calipers?

OK, I have been trying to figure out what master cylinder I can use to replace the one on my XJ750 Seca. I would like to be able to use the anti-dive thingy it has. Anyways, I was comparing calipers with the XJ550 to see if the caliper piston was the same size. The parts diagram shows that the 750 uses the same caliper assembly and seals as the 550 but then it lists a different number for just the piston. What could the difference in the pistons be? My thought was that if the pistons are the same (or same diameter) then they use the same amount of fluid so my master cylinder has to be a little bit bigger so that it powers both the piston and anti-dive. Does this make since or am I making this more complicated then it needs to be, lol?

I bet this just sounds confusing and I am way off so yeah, I don't really know much about brakes, somebody want to explain them to me :| ?

 

I think the best bet would be to get one off a Seca 650. The master cylinder on the Maxims is designed to be flat with their tilted bars.

The dual disk system (Seca 750/650) and single disk (Seca 550) SHOULD be master cylinder piston size. Because there's two caliper pistons to move, the master cylinder needs to push more fluid.

 

I'd buy the dual-disc master cylinder from PartsnMore online for $76 built for the XS1100. Should give you much better response than stock. I'm putting one on my 650 Turbo this spring.