For the heterodyne type all the systems that I am aware of measure the local oscillator and either add or subtract the IF frequency depending on wether the local oscillator is below or above the received frequency. The normal is to have the local oscillator above the received frequency + the IF frequency, but I have seen it the other way where the local oscillator is below the received frequency - the IF frequency.
I am not sure how you would do it for a regenerative receiver, as the detector is actually oscillating near the received frequency.
I bought an assembly several years ago from a fellow that built some assemblies that does exactly what I described for the hetrodyne type receiver. I'll see if I can find the information for it. It was good for a great range in received frequencies and IF frequencies.