Hi!
As been said earlier use 1500 to 2000 3M wet and dry paper and then polish the surface with 3M finess-it (1-2-3) polishing compound ...I use No 2 and 3 only. This is the professional metod...400 or 600 paper is way, way too coarse and you will never achive a mirror surface.
Done it on many pylonracers during the last 20 years.

Regards!
Jan K
Sweden