Digital BW, The Print

Hello, i scan historic negatives professionally.  It is not unusual to have
excessive grain in 1930s miniature and medium format negatives, at the time
most photofinishers did not use a fine grain developer.

You can select the sky, make a new copy layer, and shift the pixels
slightly.  This does a lot to break up the grain.

You can also apply selective blurring or unsharp mask.  You can even apply
it globally and use the history erase brush to restore sharpness where it is
appropriate.  

good luck
Thomas Robinson