When I did the walk in 2014 we found that the Southern Grampians 1:50 000 map, together with the Parks Victoria walk notes (
http://parkweb.vic.gov.au/__data/assets ... ention.pdf) was all that was needed.
I also had notes of the walk from both Glen Tempest's 'Daywalks around Victoria' (along with the gpx file previously linked by neilmny) and 'Discovering Grampians-Gariwerd' (also prevously linked by neilmny) although apart from some fireside reading, these were not needed. Tempest's gpx file was accurate, although it starts from Mt William carpark, not from Sheep Hills Carpark (the walk from Sheep HIlls Carpark to Mt William is along a very obvious track).
The only issues(?) we had navigation wise was not immediately seeing the painted arrows or stone cairns when climbing up onto the Plateau from Boundary Gap and from there to the First Wannan Hiker Campsite - and then it only took us a minute or so to locate the next one.
You have me thinking that it is overdue for me to head back there again. It's a great walk!