What follows is all unofficial and you are to proceed at your own risk!
MAKE BACK UPS!!!!!!
The DC3, in it's current state, is unsupported in XP11. Although, for the most part, it appears to be working.
You definitely need Gizmo to run the DC3. Removing it will disable, as you say, engine start and various gauges.
I wouldn't change anything in the obj files just yet. Even if it is just making changes to get shine and reflection. If you're getting ideas from other people, then proceed carefully!
To open an aircraft in Planemaker, Open Planemaker and load the .acf file. Then hit "File" and "Save". Then Exit.
FYI...An update is coming and is getting very close to completion..