The only difference I'm seeing is the location of the sound-hole w/ a slightly smaller diameter (3.75"). The bridge location is measured out at 24.9" & is at same place as an OM. Would this be correct...? And...which x-bracing would be the best option for a Triple-0 for optimum bass response. The top is Adi and so will be the 1/4" bracing. Plowing through Martin's bracing library, it seems X-brace locations for 000's are all over the place...!
If the X-brace was moved even further forward towards the sound-hole, would it's legs interfere w/ the transverse brace...

The 1st pic is from the library & shows an original pre-war 000-18 (left) & a 000-18 GE on right
The middle pic is a discarded 000-18GE top
The bottom pic is someone's drawing, also a pre-war 000-18 ('39)



Top replacement for a '70 000-28...

One difference I'm seeing between a 000=18 & a 000-28, the 18 has only 1 finger brace on each side, while the 28 has 2 finger braces .