I thought I'd follow up on this with my "progress" in this hybrid endurance thing. I haven't been able to follow the schedule I posted originally to any great degree. Over the last 3-4 months, though, I've done the following:
-About 2 runs per week in the 4-6 mile range, occasionally just one
-One lower body strength-focus day per week: usually front or back squats, occasionally power cleans or deadlifts
-A lot of KBs and metcon circuits: some common themes are variations on Dan John's "Big Five 55", lots of stuff involving KB swings, KB C&Js, weighted pullups, weighted dips, some rower sprints. I have been focusing more on trying add weight in the circuits rather than dive deeper into cardio hell.
-3 runs in the two hour range
-1 run/hike in the 5+ hour range that felt very good and was a decent time (for me) for the distance/elevation.
During this time I hit a PR in the deadlift (275), a PR in the weighted pullup (+105), and tied an old PR in the power clean (155). My bodyweight fluctuated between 150 and 155 at about 5'10".
My conclusion based on the 5+ hour effort is that it is possible to do relatively little endurance work and still feel good on long efforts, as long as that long effort happens occasionally; I think the occasional two-hour runs really helped my base.
I'm going to cycle in sprints (done in the form of Litvinovs) and try to do one long effort every 2-3 weeks for the rest of the summer and see what happens.