OK Cowboys, I need some help with this one. Dropped D-16 Strap failed. Bad back cracks. Lining compressed and cracked in multiple places. Can't get rosewood back down into place due to compressed side/lining. Brace loose/separted from back. It's down low on the bout, so I can't reach it. As you can see, binding problem too.
Correction: it's sapele
If it were me I would take the back off and repair it all would be a lot easer. Bill...
That's what I was afraid you'd say
I also agree but that's because I have large forearms and can't get my hands far inside of a guitar.
Pulling the back will allow you to check all the bracing and, should you be so incline, it will allow you to add some cross bracing to the sides while you are in there. I don't think much of Martin cloth side "braces" and have seen too many Martins with long splits in the sides.
Actually, it looks to me like the binding may come off fairly easily and the back shouldn't be too hard after that. In the end, it may also be the fastest way to do it.
This should be doable without taking the back off. If you can't get the crack together consider cutting some of the wood from inside out using a thin blade inserted on an angle. Sometimes a less is more approach will get things to align, if you can get them to align you can then add some support from inside with cleats and patches.
Gluing down the back brace can be done a number of ways.: you can wedge dowels in using ruler sized piece of wood with a hole the size of the dowel so you can reach it from the soundhole. I made up a tool for a repair that was a small block of wood with a dowel sized hole and put a spring in the hole so the dowel was spring loaded.
When working on a hard to reach place I sometimes clamp the neck of the guitar finger board down to the top of my gobar deck. I've cut long U shaped plywood cauls to get at a hard to reach brace it allows you to clamp from the top of the brace to the back of the guitar.
I had one recently where it was easier to replace a section of lining/kerfing than it was to fix it. I used the carbon fiber like rods that come with a cheap kite to clamp it from the inside.(shoulder to lower bout) Kind of like using the inside of the guitar like a gobar deck. The binding just needs to be glued back after the other stuff is done. A webcam can be a big help too.
There's a few of my moves, good luck.