FWIW, the MC16 pipes are indeed different diameter to the MC21 pipes. I ended up putting a set of unknown aftermarket cans on the 16 after grinding the pipes down. The Tyga cans do fit the MC21 pipes, tho I also had to elongate the holes on the standard flange as well as cutting a sort section off the pipe end to allow the tyga cans to bolt up tight to the flange.

Cheers, C13