You can run a 3.3v chip on a 5v board just fine in most/all cases. I grant that this probably isn't good for the chip, but it does function. Maybe my Am5x86 was especially hardy, but before I realized that there was a voltage disparity I'd put it in a 5v Socket 0/1 system, and had been running it for months that way. I figured "what the hell" and kept it in there until I could get an appropriate upgrade chip (and eventually a POD83, sometimes I swap between the upgrade Am5x86 and that.. I love advanced 486s.. speaking of which, I gotta get myself a Cyrix 5x86 100 and 133mhz to add to my experience with the various late 486 chips. :3).
Also, though this has been said in various ways in the thread, I'm not sure if it was gone over like this:
A 486 board with multiplier selections is *not* the norm - in fact, I've never seen one. 486 chips with multipliers are all internally multiplied AFAIK, and some of the more advanced motherboards that understand multipliers/etc. send things automatically (as you put it) from the BIOS/CMOS, which the chip can then interpret. However, most boards don't even have that, nor the jumpers, they just rely on the chip's internal workings, because that was the norm for the vast majority of the earlier 486 boards, and these were upgrade chips (yay run-on sentence!).
As such, ignore the multipliers. Use chkcpu (
http://web.inter.nl.net/hcc/J.Steunebrink/chkcpu.htm) or a similar tool to check the speed and specs for the chip, once installed, and you'll know whether the multiplier is working right, as you know what the FSB is I'm sure (and usually that either runs at a fixed speed or *does* have a jumper - most often 25/33 selectable, with better boards having 25/33/40/50/60 or 66 or combinations thereof, and the earliest 486 boards running at 16).
Excuse my rambling, but I love 486 machines, hah. I hope some of the information I spouted here was useful, and if you'd like clarification don't hesitate to ask :3