Here is the way to do it:
1.Delete the solid body in order to keep only the surface
2.Calculate the diameter of the holes. I calculated 50mm. Then use the surface fill command to close the holes.
3.Use the surface flatten command and use the selections in the attached picture.
4.Use delete bodies to remove the curved surface. Then open a sketch on the flat surface and convert entities.
5.Create a base flange in sheet metal using the sketch. Then cut the 2 holes you removed in step 2. In order to place them draw a 3 point arc on the curved edge and make the cuts concentric.
6.Export a dxf flat pattern for cut.