I have one that's not a hybrid. It's a stressed tree in blight range (Hunterdon, NJ) but it soldiers on. Last year I got a few dozen chestnuts off of it. Normally I can only get a few.
(I also have two seedlings sprouted from chestnuts I gathered a few years back)
See my other more recent comment for more details. It's old. I'm not so sure it has resistance other than it was likely a strong adult when the blight came, and the blight had an easier time killing trees that were not so massive.
Before I made last comment I tried to wrap a measuring tape around but it was only a 36 inch measuring tape and circumference of the two halves coming out of the base are at least another 6 inches after it. Height is harder to measure, maybe 30-40ft, it grows at the edge of the forest with multiflora rosebush around it, some hickory and tulip trees over it in height. Some branches have been cut off over the years and the bark is kinda gnarly.
Everytime I walk around here there's some new discovery of something new or old. Today I fished a live rusty female crawfish out of the pool and I'm pretty sure it's one of the first sightings of this invasive in this county. Nothing like looking down and going 'Oh I guess we have pool lobsters now'.
(I also have two seedlings sprouted from chestnuts I gathered a few years back)