Main set,
4 blocks of this:

100 kick,
300 free with pull
30 seconds rest

100 kick,
200 free with pull
30 seconds rest

100 kick
100 free with pull
1 minute rest

THe kick is fast, as in this is not social kick, time it if that will help you, should be about 10 seconds slower than your regular 100 free. Your legs should be very tired after only one hundred, thus the pull for free...
The free, faster as the length goes down, so the last 100 should really be fast.