While netsurf seems to be a good candidate what about OWB/Odyssey? I don't know how modular it is, but stripped down (JS & some other cpu demading things disabled) I could imagine it could work on higher spec'ed 68k machines.
Either AROS OWB or Odyssey could be good starting points for a stripped down OWB 68k version.
But probably netsurf is the better starting point as there is a working 68k build already.
