With an Advance Design COE the parts of the cab that are different from a pickup are dash board and seat forward. Everything rearward is the same on a COE and pickup or truck.
On a panel or Suburban, everything forward of the doors is the same as a pickup cab.
Conceptually you can separate the COE specific pieces and graft them to a Suburban or panel to create a COE Suburban (concept on one of my projects) or COE Panel.
I'm wondering if you could apply the same ideas to converting a conventional Art Deco bus body into a COE Bus, and then fit out the bus body as a motor home.
Just thinking at the keyboard...
