748r etc using 4 pad callipers
 

Does anyone know if the models like 748r that use the 4 pad callipers, have a different master cylinder to the std 2 pad bikes?

No, I don't know.

But, I upgraded to 4 pad calipers on my ST and they are quite happy with the standard ST master cylinder so you probably don't need to change it

What about the size of the bore then?

If you are still using a four piston caliper then the original master cylinder should be ok, you will of course benefit by fitting a later more up to date master cylinder.

The only time you really have to change the master cylinder is when you change from a two piston caliper to a four piston type, then you need the extra capacity/ratio of a master cylinder suited to a four piston caliper.

As a point of interest, I chnaged the original 2 piston calipers on my Jota to four piston Brembo`s and fitter AP Lockheed ajustable ratio master cylinders which I can only praise in terms of performance and quality of construction.

Back to the original question, the M/C is the same.