Brake drag
 

Whats the most likely cause of front brakes dragging,wheel not rotating freely when spun by hand.Will discs/master cylinder from 748/9.. fit.

Two things that are most likely are warped discs or sticking pistons.
Check the first by spinning the wheel with a pencil or such like held against the fork leg and just touching the disc. Spin the wheel and see if there is any discernable warp in the disc.
The second, most likely IMO, is you have a sticking piston or two. There's no service kits for Brembos, but with care you can take them apart, clean them and reassemble with some rubber grease.
The other thing to check is that the wheel is centred in the forks. Undo the axle pinch bolts and work the brakes a few times, bouncing the front end, then do the bolts back up.
Check the pads are wearing evenly. This is usually a good pointer that something is sticking or out of line.
There will always inevitably be some drag on the brakes. Fully floating discs remove some of this, but still not all.