I clearly need to review my route vs. distances....
my map here I just found this video of the Great Alpine Road from Wangaratta to the coast via Mt Hotham - it's only a 360km day for me, but I'm thinking it will take all day: go slow, keep away from the edge and the oncoming traffic

, and stop lots for photos... I have high expectations for this road

Wow!
However, I'd planned on mostly half-day rides - so I need to check more of the squiggly bits to make sure it's all achievable.