[Patrick]

Are the FD mounts those rings that clamp around the motor? If they are then they probably won't fit a neu.
Feigao and most other smooth can 540/550 size motors are 36mm diameter.
Smooth can neu is 39.6mm
Finned neu is 43.8mm

For 5s you could use the 1515 1y (2200kv), 1515 2d (2050kv) or 1515 2.5d (1650kv), just depends on how much power you want, and if you can get a motor mount to work with a neu.