[Chas]

I use caution when replacing defective mica caps in frequency determining circuits. Often, they have a tempco even if not marked so the tuned circuit stays stable as the coil drifts with temperature. The earlier the radio the more likely the component is "house marked"

Same applies to the "dogbone" ceramics these are often tempco any more than three dots are suspect but where it is in the circuit is often a clue.

One of my first re-capping experience (1965) was with a Hammarlund SP-110-x horrible drift and unable to calibrate the center of the bands both RF and oscillator circuits. The OEM open mica caps were of a special brass/steel clinched (liken to bi-metal) construction that remained stable. However, time and moisture ruined them. Finding suitable values and temco was cut and try, the schematic available did not give values, though I no longer remember the value they were N330.

IMHO I do not think drift in a 455khz (sic) IF is a problem, I have not noticed it, but drift in a receiver that uses a higher IF such as a dual conversion drift in the IF is suspect.

The "discovery"  of what appears to be a sure thing replacement for a mica condenser should not be an excuse to shotgun.

Chas