Rachmaninoff 3rd Concerto, 3rd movement

I’ve tinkered with both C flat and C natural in this group and the next, and I cannot decide what to do…each of the 3 scores I own has a C natural in both groups, but the bar before 54 (the poco a poco accel) has a C flat which sounds so rich and sombre…should it be reflected in this little fragment too? Is it just a subtly different harmony and a Rachmaninoff trompe d’oreille…? Anyone have any thoughts? I don’t understand his harmonic logic to have a C natural here.