I'm not a coach but I am capable of observing workouts. When I was in college at the beginning of the decade I had several teammates under 1:50, the fastest being 1:44 in the 800. And a few 45 second 400 guys.
The 800 guys would have their longest run of about a 4 mile temp, giving it a true tempo effort of about 5:20's per mile when they could certainly race a 4 miler at 5 flat pace. Their longest track workouts would be repeat 1k's, or occasionally intervals as long as 1200 meters early in the year. They would do 5-8 of these reps around 3 minutes for a kilometer with a fair amount of rest.
The 400 meter guys didn't do any tempos, but they'd do some longer progression reps of 500 or even 800 meters, picking up the speed as they go. Or they'd run some repeat 300's at a prescribed pace with significant rest, not all out but certainly faster than their 800 meter pace would be. A 500 meter time trial in practice was common for the 400 meter group at early in the season, but after about a month of practice or so.
The biggest distinction between 400/800 guys and distance guys is how much they lift. They were in the weight room twice per week and putting up some serious weight for track athletes. None of them could run good 1500's though, one of the 1:48 guys ran a 3:52 1500, the 1:44 guy ran a 3:45 or so. So their training didn't help too much for endurance, it was very focused on 400 and 800 meters speed, probably because of the amount of muscle mass.