Yup. That lean-to was still there (NE quadrant of intersection, shown on 1963 AMC map) on my first visit to Mt Isolation in 1965, on an epic day hike with full external frame backpacks that began with an Audubon Society bird walk in the Great Gulf, a terrifying ascent of Six Husbands Trail (we left the bird walkers behind), a traverse of Mounts Clay, Washington, Boott Spur, Slide Peak, and Isolation, and descent with Justrite headlamps (four D cells, mail-ordered from Campmor!) to Rocky Branch shelter no. 2 where we met two friends with the homemade wine who had hiked TFW earlier in the day. Mounts Ike and Pierce were Mounts Pleasant and Clinton back then.
That's quite a day hike! 4 D cells? We used to lug a 3 burner Coleman stove (with 1 gallon of fuel) on 5 day-4 night trips. Kind of a hassle, but we always had hot food.