[Radioroslyn]

You can use 2 .0068 or .0075's. Values isn't super critical, it's used to quench the high frequency response  which helps keep the audio output stage from oscillating. Have seen caps as large as .02mfd in some circuits. With that large of a cap it tends to make the audio sound muffled. Another reason why a larger value is that it gives the appearance that the set has more selectivity by eliminating the audio portion adjacent station splatter. Sometimes I'll adjust the value a little to .01 or .005 it really brightens up the sound and sounds louder. Disc caps are fine too. If you are into restuffing the mylars are easier to work with, you probably fit the two into the old cap casing.
That's the longer answer.
GL

Terry