I have 2 of the Fox 40 from the 1970s that is shown, they run very well, and I had a flying partner that used one on a large airplane, t was large back then, a 54 inch chipmunk wing with a larger fuse, so iit was a good bit larger than a Nobler, and over 600 sq in, the FOX used a Rev-Up 11 x 6 and ran a nce 4/2 , Pulled the airplane with pretty easy, and was good in winds. Not as powerful as an HP40 or ST46, but much more power than a Fox35 or OS 35-S , Closer to the power of a OS 40-H ,
If I was to use one today, and I would put it in a Classic ship, I would use 24% oil 10 nitro, half synthetic on the oil, Yes the engine is a little heavy, and YES t runs better than the loop charged later model FOX 40s, and not much difference in weight between them
Randy