I'm not sure there is a version of HU that fits your request, although I think looking for the earliest version you can find is the way to go. Consider browsing the
PhrozenKeep mod archive, which happens to have HU v1.2 Solo Edition. If you investigated their forum, and ask which mods are similar to Vanilla but with more challenge, then you might get good results.
As far as large-number reductions are concerned, I know HUv1.7 uses smaller numbers for HP, etc, but otherwise has very little in common with Vanilla. It does have a solo version though.