I tried logging in over at the UMGF thinking that would be the place for this question but dang if I simply can not log into that site anymore
Anyway I know some vintage restoration guys are still here, calling Frank Ford, John Arnold etc... anyway. I got this old one in for a restoration and I have not seen a bracing pattern like this in any of the literature and am trying to figure out if it was modified at some point. The client wants it to go back to all original if possible. There is a cross grain crack near the tail block that someone repaired with a gigantic block of some wood but it's also possible that they added this diagonal brace too.
The center brace was also cracked and caused a dip in front of the bridge to the sound hole.
Anyway here are some pics. If you just put together these two pics you can see the whole bracing. The guitar is so old that I cannot take a pic with a bright light source inside to 'ghost' the bracing. The spruce is like torrified wood that is opaque to light.
Regards.