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I do have a Nano running at 3.3v and 16mhz, seems to work fine.

I'm getting by with a kludgy 3.3v regulator for now,
but buying some AMS1117-3.3v regulators in the SOT-223 package:
That should make it a fairly clean conversion.

Here's the Nano CH340 clone schematic:
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Procedure:
? Replace the LM1117-5.0 regulator with a LM1117-3.3 (or AMS1117-3.3) regulator in the SOT-223 package.
? Cut the trace to cathode pin of the SD101CWS diode free of the 5v rail (anode pin still goes to the USB connector)
? Add a wire from the now free cathode pin of the diode to the VIN header pin (trace goes to input to the LM1117-3.3)
? Add a wire from the 5V header pin to the 3V3 header pin.

Here is why we connect the 5V and 3.3V header pins:
The CH340 USB chip is normally powered from a Vcc of 5v,
it has a regulator inside to power the 3.3v core logic inside the CH340,
and perhaps some very light external loads of 30ma or less.
The CH340 chip can also be powered from a Vcc of as little as 3.3v and still work,
but then CH340's Vcc and V33 pins must be tied together to avoid the internal regulator's dropout voltage.
The CH340's Vcc and V33 pins are connected by traces to the 5V and 3V3 header pins of the Nano.

If you want a bunch of 3.3v regulators, here's a source for the AMS1117-3.3:
? ? ?? ??
To remove one, I'd cut the three pins free, then put a soldering iron on the heatsink tab and
lift the part out with tweezers.? Then clean away the cut pins.
But be careful, these $2 clones use boards for which the copper pads are not well glued to the board,
the pads can easily lift up off the board when hot.

Jerry, KE7ER