Before you remove the 800 ft. board from the wall, trace the position of where the 1,000 ft. piece will sit. This will help you place that little 1000 ft. floater piece. This entire process may take several days. It is somewhat slow and tedious. It is best to have older youth working on this part - 5th grade and up.
High school is best.
We have been reduced to just hand cutting some pieces to make things fit together properly at all of the boundaries.