160/60r17 road tyre is std for most 400's, and most 400's run a 4.5 inch rim, just like the MC21.
So yes, tyre will fit and work very well. (I do prefer a 150 rear if using a 110 front, but difference is very little)
We have a 160 GPR on a MC21 rear on http://www.rpracing.co.nz/specials_nsr400r.htm Front is 120/60r17 on 3.5 inch CBR rim.
Earlier 16/63r17 (160) Michelin and 160/55r17 Dunlop etc slicks on the other hand, wont work well. These are designed for 5 to 5.25 inch rims.
The later 16/63r17 (165) Michelin and 165/55/17 Dunlop etc are designed for 5.5 inch.