So to port dillo you'd need to update m68k port of FLTK which might be possible.... I was able to compile the code with ECGS on Red Hat Sparc with a few fixes so... yeah it might be possible 
I think there was an old FLTK 1.1 binary somewhere. If you want Dillo I suggest starting from the D+ browser port... its supposedly implemented more cleanly and in a single binary unlike Dillo which loads plugins which can leak memory as well. It receives little maintenance but in reality that matters little.
http://dplus-browser.sourceforge.net/index.old.php
That said... I think Netsurf would be the better option. It already runs on Atari.... and Amiga so it might be possible. That said I think they use modern compilers and cross compile to the target machine which really would be a handy thing to have for classic macs but I don't know if it exists.
I think there was an old FLTK 1.1 binary somewhere. If you want Dillo I suggest starting from the D+ browser port... its supposedly implemented more cleanly and in a single binary unlike Dillo which loads plugins which can leak memory as well. It receives little maintenance but in reality that matters little.http://dplus-browser.sourceforge.net/index.old.php
That said... I think Netsurf would be the better option. It already runs on Atari.... and Amiga so it might be possible. That said I think they use modern compilers and cross compile to the target machine which really would be a handy thing to have for classic macs but I don't know if it exists.