If you want to be adventurous, you could do the Col du Solude first, via Villard-Notre-Dame.
It is a track rather than a tarmac road though.
How much of it is unsealed? I read it was partly unsealed, but couldn't find how much. A Col de Solude loop from Le Bourg d'Oisans is on my to-do list.
(No idea when I'd be doing it, though, given I have to travel across the world just to get to that general area)
Actually, I think I just answered my own question. As far as I can tell from Google StreetView, the unsealed part is from Villard-Notre-Dame to Villard-Reymond, about 4.2km long.