Never seen anything quite like that! Incredible! However, many older MC18 barrels have wear there, but I've never seen any actually worn through!
The barrel with the small RC Valve/exhaust ports is indeed MC16. (MC11 NS250R barrels are totally different to NSR barrels, and are finished in black. They also don't have RC Valves.)
Fitting 2x MC16 barrels to an MC18 will work, but likely see you with around 50hp. A pair of MC18 barrels is a much wiser choice, and it's worth doing the job properly.
_________________
Andy.
NSR-WORLD.COM
Please keep all responses to Forum posts on the Forum so that others may benefit.
Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.
Check us out on Facebook! Please "like" our page!