Yes. The MC21 uses nylon intake rectifiers positioned inside the reed cages, and the MC18 has the rectifier cast into the manifold.
You can use either setup on both models.
_________________
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!