As you can see, I used some of the original trim to "clean up" the look of all those rough cuts. It is simply trimmed to fit the new arrangement, in order to make it look halfway decent.
In this shot and by looking closely, you can see the lines I penned onto the overhead which show the location of the mast base pad, and the outside dimensions of the new strongback. Edit: The original strongback/bulkhead provided support only about twice as wide as the dark area you can see here. The new one will be 3 times as wide.
I'll be cutting back the overhead liner so that it butts into the after edge of the new strongback. I considered leaving it in place, but it is just too different of a shape from the inner deck skin. Also, it was apparently trimmed (sloppily) in place at the factory, and so there are cuts into the inner skin along that line that I want to repair prior to inserting the strongback.