So did it allow you to set the MHz without rebooting the machine?

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I can't know until I get a video card (until then, the machine's rather useless).

This could be a Variable Speed Overdrive that Newer Technology manufactured for various 68k machines including the IIfx. With the multiple oscillators and the wires connecting to the original on the logic board, it makes sense.

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Variable speed does make sense, but as I said above, I can't know until I get a video card.
It also has a big red momentary button on the side closest the CPU socket (see photos). I wonder what that does? I've speculated that it could be one of two things: a secondary reset switch, or a speed selector (it seems more logical that that would be done in software, though).

Once I get a video card, I will definitely play around with it and see what it does.

Until then, it's pure speculation.

c