Two performances being equivalent doesn't mean an athlete should be expected to run the equivalent time in both events. Presumably, most high school athletes running 1:17s are not equally suited to the 800m as they may be coming from a long-sprinter background.
With that said:
Mercier Calculator: 1:17.49 = 1:49.22
IAAF Points Table: 1:17.49 (Indoor) = 1:48.81 (Indoor) or 1:46.92 (Outdoor)
IAAF Points Table: 1:17.49 (Outdoor) = 1:49.17 (Outdoor)
I think it's hard to argue that a 600m on a flat indoor track is a true indoor race in this context, as indoor has historically described performances on 200m or shorter tracks. I have no idea how the physics of tighter turns impact performances, but as a rough equivalent for the 300m track you could maybe split the difference between the indoor and outdoor equivalent. Call it 1:47.85