Well last night I managed to start the cut through the cork & plaster for the downhill grade towards the bridge. The grade also incorporates the turnout from the new staging area.
The plaster sub roadbed was a good choice and allows the sculpting into various landforms easily. I have to add cork underlay again and shape that into the finished grade, the path that the new line is taking flows much better than previous and adds a nice little scenic detail with the cut.
Once the cut has been finished I'll be adding the landform base using masking tape and a coat of drywall sealer.