i Don't know if the 18 barrels have larger exhaust ports if they did it would'nt be that much difference in size anyway i mounted them onto the mc16 barrels with no problems what i have is a mc18 not a 16 the chassis are different from the two bikes therefore i don't know if you can mount the 18 pipes on the 16 chassis another hot mod for the 18 is to replace the rear shock with a cbr600 f2 unit it gives you 25cm rear ride height increase and the damping is better also you don't have to change the spring i am 73ks and it works better than the standard shock if i push on the seat with my little finger the shock responds that's how responsive the cbr shock is you have to redrill the top mounting hole not much because the nsr mounting bolt is just a little larger then get an angle grinder and shave each side of the shock to reduce it's width so it will fit in the frame it can be done by most people at home.
_________________
To be or not to be is illogical captain