Are you sure that you can use a 160v Styroflex for c17? The Neumann data sheet calls for 500v
Polystyrene film caps are harder to get these days since all but one of the polystyrene film makers closed shop. The only Amercan brand still making them is Reliable Capacitors in Santa Fe Springs, CA. Their limit is 1000 pf. Some asian caps are still available.In a pinch a good sub would be a quality polypropylene film and foil cap like the WIMA FKP-2 series. Those come in 1000 volt ratings, 100, 68, 47 and 33 pf are available values.
For example the initial U67u 00-00-00S. (Considering that 17 is the highest number for a capacitor in this model, the designation as C17 may be an indication that is may have been an afterthought...):