I may have made some progress on Site 31, but a location is still not apparent to me. The strongest signal I have observed was from above and east of McConnellsburg, PA on Aughwick Road. I had signal near McConnellsburg and Hustontown, but it was spotty, and the primary coverage for these areas would be from the McConnellsburg and Butler Knob sites, respectively. It seems Site 31 is at a more distant and perhaps higher profile location.
From the coverage maps, there is a Broadtop site shown, which from the map appears to be near Broad Top City, PA. I'm having trouble reconciling that as Site 31 since I had only weak signal from US 30 atop Sidling Hill, and along the roads towards Waterfall, PA from there. On the wiki, Broadtop is attributed to Pine Grove Mills. Broad Top City is also relatively close to Butler Knob. Perhaps it was changed out as the network expanded.
Based on gaps in the map, southern Bedford county and northwest of Huntingdon may be good candidates for the unknown sites.