I'm stuck at the same point. I can't see an easy fix in the minetweaker scripts - I'm not sure why greatwood is in the plank oredict. I did a hacky fix though, by adding
recipes.addShaped(gwSlab, [[gwPlank, gwPlank, gwPlank],[gwPlank, gwPlank, gwPlank],[gwPlank, gwPlank, gwPlank]]);
to the...