High 1st IFs like 55.845 MHz aren't quite uncritical, particularly with
very compact receivers

That's high?

My radio's first IF is 240.1 MHZ.

you easily get leakage around the 1st IF
crystal filter.

Good information. I didn't know that before.

And just the other year or so, I didn't know anything about IF frequencies or
radio image frequencies.

I still don't know much about them.