Wekk first of all, what is your current training structure? Are you following a Charlie Francis template with alternating low and high intensity days or are you doing something else?
Another thing, how much longer is your season since you’re already in SPP? If its less than 5 weeks I’d follow what I have here and then have your runners taper for their peak. If its more than 5 weeks you would probably want to change it as time goes on so they dont get stale from the same training on the same day of the week.
Also, (I dont pretend to be an expert here but…) I think you can follow a Charlie Francis template using your beliefs in terms of training. You can use maybe something like this (just a sample)
Monday: MaxV (your runners are fresh and so it would be a good idea to develop this here, also, acceleration and decelerration are all on a percentage of your overall MaxV for a 400m runner, so a runner with a high MaxV would have an advantage over a runner with a lower one)
Tuesday: Extensive Tempo (here you can really get your runners acclimated to longer runs by doing distances of 500 or even 600m at about 70% for an overall volume of about 2000m)
Wednesday: Special Endurance (This is where you really develop your race, maybe have your runners do 2*420m in racelike conditions with full recover [read:35min+] between runs)
Thursday: Extensive Tempo (do less volume today after the intensity on the CNS the day before, possibly 400m or 500m runs at 60% for a total of 1500m)
Friday: This would be like a wild card day, if you notice a runner is weak in terms of overall speed then have them work MaxV. If a runner needs to work on endurance maybe do a workout similar to Wednesday or even consider intensive tempo (possibly). If you see a runner is still fatigued from the preceding workouts then have them do a short extensive tempo session and send them home to rest.
Sat: Extensive Tempo similar to Tuesday (or give runners day off, depends on how they feel)
Obviously you would want to include weights or training with Med balls at least twice a week (3 for more advanced runners) on your intensive days.
This is just what I think, and I could be completely off base, so anyone else feel free to comment or correct me.