That is a really cool photo of the interior of your X500. It is interesting to see the kerfed, rectangular foot-plate glued to the arched back (and probably one on the top as well). I believe that this is the same wood-working technique used to glue the center-block to the top and back of the Starfire IV, V & VI (as well as the ES-335). But the foot-plates and block run the length of the guitar, obviously.
I had noticed the two sound posts "just north of the f-holes" on my '59 CE-100 DP. But I was never sure if they were original to the instrument... or installed by an enterprising previous owner. The type of wood, and the unfinished saw marks, seem to match the parallel (really A-frame) bracing.
The Gretsch 6124 (single Anniversary), listed below, has a true maple trestle that runs from the neck block to underneath the bridge connecting the top to the back. It makes the guitar a lot heavier than the Guild!
I don't play either guitar outside of my living room, so feedback really isn't a problem for me.
Bill