Don't be surprised if you can't get the 4x multiplier going with the 5x86 installed. For whatever reason it seems to be an occasional issue with OEM BIOSes.
If your board is really from 1993, I would steer clear of the POD upgrades. Even boards from 94 and 95 can struggle with those.
You should try to determine the source of the clock signal on your board. Does it come from an oscillator or a clock generator?
I suspect the clock signal can be changed with minimal soldering. 33MHZ bus should actually give you a pretty noticeable speed boost, but if you have 25ns SRAM you'd definitely want to replace that too.
If I had to guess, I'd say that IC sitting next to the crystal is likely the clock generator. If you can read the model number on it, you might be able to figure out what the pins do, and it's possible that you can change the speed of your board by either removing or adding a 0 ohm resistor. If a 33MHz version of your board exists, you can probably figure out what to do just by comparing these two locations.
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