It's a bit more difficult.
The standard VGA registers allow a wide variation of modes and timings. Essentially you can use any frequencies you want, within the limits and resolution of your specific card.
Early analog monitors are different: Some have fairly tight restrictions on the frequencies and timings they accept. So you needed to program the registers correctly for your specific monitor.
As this wasn't very practical, there were three approaches to make it simpler: The first was to standardize monitor timings. The second one was for the monitor to tell the computer which frequencies it supported (the protocol is called Extended Display Identification Data, or EDID). The third one was multisync monitors, which accepted a range of frequencies, were fairly lenient about details in the timings, and offered monitor controls for fine tuning.
So the question "what are frequencies of common tweak modes" in this form doesn't have an answer. You can "tweak" the standard modes, keeping most of the timings. You can also figure out what timings your specific monitor supports, and make specific custom ones (I did this a lot, with even "funnier" resolution than the ones you mention; it's easy under X on Linux). Or, with a multisync monitor, you basically don't care.
But there are no specific frequencies that would somehow apply to all monitors.