I am experimenting with fitting a 6 kHZ Collins Filter to the 455kHZ stage of my home built Wadley Loop receiver. The filter is fitted in between two back to back IF. transformers after the mixer. I have employed a bit of estimation to try to get a good impedance match between the transformers and the impedance of the mechanical filter. The filters own resonance is not quite centered on 455kHZ, so the IF. strip is adjusted to the filters frequency. The response and shape of the trace looks good. The receiver works well.