Yes, I glanced through the motherboard's manual when I made that post, but all it seemed to say about the configurable voltages was "what was allowed by the particular CPU being used." So I'm not sure whether the bios has any restrictions in place or will allow you the full range of the voltage regulators regardless of the particular CPU, or how low it can go.
Some light googling basically showed people trying to find the 160u/260u series and the only consumer source they were coming up with being ebay, where all I could find from a quick search were the 260u/270u (which have higher TDP than the 160u/170u, but you might be able to disable a core in bios, since that's all the 160u effectively is apparently) from HK. If it were me, I think I would give undervolting/underclocking one of the Semprons a try. They're already over 50% higher clocked than the 160u, scaling that back to comparable clocking alone should reduce the heat output reasonably, depending on how low they'll undervolt at that speed you may be able to get them down to about the same as the 160u. Especially since they're only $36 shipped ^.^
Unfortunately I don't have any actual experience with using AMD platforms for this type of situation, so I don't know the voltage tolerances people have been able to use without doing some research. I've managed to do it fairly well with a couple different intel platforms. Are you going to be using passive cooling?
Also, depending on your situation, one solution that can actually be fairly cost effective for something enclosed with low heat dispersion is procuring a used/cheap replacement laptop motherboard with ULV CPU. But you already said you had a motherboard, and I assume a case/etc for it, and using a laptop is fairly limiting in certain ways.
Hopefully all of that is helpful in some way =)
