I had 2814/11s motors on my DJI F450. I used 10x4.7 APC props with a 6000 mah battery. I didn't use extensions. You'll need them if you go 11 inch or higher. My craft flew perfect. I had to test the WKM after a prop break induced crash totaled my flat hexa. The WKM and 4 out of six motors survived.
I dont think I had to modify the mount holes at all.