One of the differences between track and road frames is that a track frame will have a higher bottom bracket, to reduce the chance of pedal strike. Since a conversion is based on a road frame, this becomes a factor. There are several ways to minimize pedal strike:

1) Use shorter cranks; you can get them as short as 165mm in road/track type, and as short as 150mm in BMX
2) Use larger tires, because they will also be taller.
3) Use narrow track pedals or clipless
4) Use flat arm cranks and the shortest possible axle to move the cranks as close as possible to the middle of the bike frame (small Q-factor)