I had a K-45. They need low nitro, 10-20% and a lot of oil, again 20%. I didn't like the needle bearings on the con-rod as it kept spitting them out. After tossing the bearings twice I ditched it.
Engines are currently being remade, Frank Werner user name D-7 is making them, i've just ordered my second engine, initial testing shows great promise. Very happy with the K45 awsome engine.
I ran the K-45 for several years using a titanium connecting rod. I used one of Kalistratov's billet pistons and 60% nitro. The drum rotor turns on a bearing instead of a bushing. Very nice engine.