Clyde Hart’s training is good, however his training is focused on athletes with 46 400m speed. It doesn’t mean it wouldn’t help you though, but developing speed would be better for you in my opinion.
Basic week could look like this -
Day1: 1.5 mi warmup / drills, 4x800m focusing on form and having a consistent pace t/o the intervals...3x100m strides, 1.5 mi cool down...core, stretch.
Day2: AM Lifting/stretch, (power cleans, front squat, calf raises, etc.)
PM 1 mi warmup/drills
6x strides 100m (2, slow, 2 building, 2 quick)
Repeat hills (Find a long incline in the road or a steep hill, 150m+ hill/road if possible...OR stadium sprints) basically for the hills you want to have 3 different paces. A tempo pace going up the beginning of the hill, and then 95% effort at the incline and maintaining good form for explosiveness. Then, a recovery jog back down and repeat. Stadium sprints Same thing, hard pace up, slow jog back down.
Day4: same as day 2 (except lifting is hang snatch, GHB raise, box jumps, step ups, etc.)
Day 5: 6x60m sprints (2 standing start, 2 falling, 2 3pt start) all out full recovery.
Then do medicine ball throws for explosiveness
Day 6: lifting (back squat, bench, pull ups, shoulders, curls, etc.)
Active rest, bike slow, easy run, or just do some core/rolling out
Do this for about 10-12 weeks and then you can start doing more speed stuff. Core/stretching is essential for 400m runners, as you typically fall apart the last 100. You don’t wanna do too much speed too soon or you could injure yourself like I have, or burn out. Lifting is big for 400m guys, so make sure you aren’t sacrificing form. Ive ran a 48.6 and just started to train again after I got two stress fractures.
This is basic and you could easily change whatever you want, but it’s worked in the past for myself and others. Pre comp/comp phases I can type out later if you want.