I’m reasonably certain, Wells would have gone 50/20/50.
Fast for the first 50m - ease off as going through the tape or coast for 20m, then hard for another 50m.
This is a ‘stock’ session Wells would have adopted from his coach Wilson Young.
A normal session woul be 6 x 50/20/50 in two sets of 3. Walk back between reps and 10 min rest between sets.
During the specific prep phase we would start with 6 and over several weeks work up to 12 (2 sets of 6).
These would be flat out from blocks with a gun or whistle start. Tough session but the athletes if conditioned properly over the previous months, should be able to handle it.