Begin your buildup with a relatively easy 4 weeks of just jogging, increase mileage to 70-80% of what you were doing in cross. Then, begin pure speed work: once a week, do short hill sprints with FULL recovery (3 min). Do no more than 6-8. After a few weeks of hills, turn half of the weekly speed sessions into flat sprints, starting at 40-50 meters, working up to 120 meters over the next few weeks. By the time you start the hill sprints, you should have also started some basic aerobic work. Do broken tempos at around half marathon to marathon pace and 1k’s at around 10k - this is all you really need for your events. Make sure not to overdo aerobic work as it can negatively affect your 4/8 speed. As for the specific 4/8 workouts, leave those to your coach, but they should be pretty simple. Also mix in some 200s at mile with 200 jog (rhythm work), this is quality aerobic work that still touches your fast twitch fibers.