you are basically talking about me back when I ran in high school. I played football all 4 years and was a pretty good 200/400 runner until I switched to the 800 my senior year and ran 1:54 on maybe 20 miles a week at most.
Having learned alot about the event through running at the college level and coaching it at the high school level, the 800 is truly a speed event although many still do not see it that way, especially at the high school level. The fact of the matter is that sprinters do not want to run it or do not have the mental toughness/speed endurance, and the distance guys dont have the wheels.
You can be a really good high school distance runner and maybe get under 2 minutes or close, but if you really wanna be good at the 800 (1:57 or under for high school) you will either need to have EXCELLENT endurance (4:20/9:20/15:30) or a level of sprint speed far superior to your average 1600/3200/5k kids/cross country runners.
Although a speed-based 800 runners overall endurance may be inferior, it is alot easier to run a 1:56 (2 58 second laps in a row) if you can sprint significantly faster than a 58 for an open 400 as opposed to having to sprint the whole 800 like most distance guys have to. For example, a good high school distance runner might be able to run a 2:00 off a 55 second 400 PR, but those 2 laps are going to feel alot more uncomfortable if he has to run close to his top speed the entire way. In comparison, when I was in my tip-top 1:49 shape I could literally jog a 54 despite being a pathetic 5k runner. It is alot easier to teach a fast guy endurance with basic tempos/longer runs than it is an endurance guy to be fast.
If you want to focus on the 800 you really need to work on your top speed.