I picked an existing non-default directory to install the 3185 build, and unticked the create icons, etc., tickboxes. The installer then forces you to pick somewhere for a Start Menu entry. It then secretly appends that to the install path previously entered! I didn't discover this until I ran it using the existing shortcut and still got the previous version - the new one had installed itself in a subdirectory off the old version.
I reinstalled and after the forced start Menu entry, went back and edited the install path to remove the incorrectly appended entry. It then installed correctly, but unfortunately, proved to be pretty well unusable :(