Day 1:
Meet in Michigan City - Ride coastline to H-D Museum - Dinner in German Town (I know a good spot)
This map lies,,,it's really 8 hours (From my house) not following 94 the whole way. Figure +2 hours for you day 1?
Day 2: 10 hours without counting stops? That's more like it!
Head up the Kewaunee - Lambeau Field - Escanaba - Sault Ste, Marie
Day 3: Leave the Sault - Cross the Bridge (No eating in St. Ignace at the shitty place with the awesome view!) - Check out wilderness State park (I left this day shorter to kill time here & make up for the long haul of day 2) - Legs Inn! - Tunnel of Trees - coastline around to the Dunes and finish in Manistee or Ludington (7 hours)
Day 4: Luddington to Michigan City: taking scenic road as much as possible (4 hours) - Split and head home.