If I remember correctly, the polystyrene caps were about 1.5 inches away from the edge of a roughly 5 by 14 inch 4-layer board.
I have beautiful General Radio decade capacitor boxes and lab-standard single units. They made both polystyrene and silver-mica versions (as well as air-dielectric singles), and the catalog listed the pros and cons of each. Basically, they recommended polystyrene for low-frequency applications, since the "apparent capacitance" of the mica caps increased at low frequencies. Hermetically-sealed polystyrene caps hold their accuracy: I found no errors measuring them with more modern equipment.