How I did the 1970 Guild D 40 neck reset without removing the neck, the strings being almost 5/8" from the fretboard at the fourteenth fret.
The bottom of the fretboard had dived into the body, the neck had pulled away from the back of the guitar at the heel and had actually sunk the shoulders of the D 40 slightly from forty years of string pressure. Additionally, the neck was twisted about 3/8" down at the treble side nut.
I first took an 1-1/2" steel slightly flexible 'L' bracket, the kind found in hardware stores, and screwed it with the horizonal side up (with a coarse-thread drywall screw, through the soundhole with a very long driver bit) to the bottom of the neck block.
I then cut a pine block slightly smaller than the distance from the top of the 'L' bracket to the bottom of the ladder brace at the top of the soundhole. I cut a thin, gently tapered wood shim and drove it between the pine block which rested on the 'L' bracket, and the bottom of the brace. I tapped the shim a little further each week for about six weeks until the bottom of the fret board was just about even with the rest of the fretboard. The bracket, pine block and shim will, of course, remain in place. The strings were still a bit high, and any truss rod effect was maxed. The original bone saddle was as deep as it could go, so I belt-sanded off an eighth-inch of thickness from the forward part of that big, thick Guild bridge and reinstalled the saddle, the bottom of which I had also sanded down an eighth. I had to re-taper the bridge pin holes, but when everything went back together, the strings were just about right. The twist in the neck, which is down about 3/8 on the treble side from the nut, well, it just takes a slight wrist position change on lower barre chords. The guitar is now quite playable and the strings are about 1/8" at the fourteenth fret . Surprisingly, the tone was not affected by all this meddling. Hope this helps.
The bottom of the fretboard had dived into the body, the neck had pulled away from the back of the guitar at the heel and had actually sunk the shoulders of the D 40 slightly from forty years of string pressure. Additionally, the neck was twisted about 3/8" down at the treble side nut.
I first took an 1-1/2" steel slightly flexible 'L' bracket, the kind found in hardware stores, and screwed it with the horizonal side up (with a coarse-thread drywall screw, through the soundhole with a very long driver bit) to the bottom of the neck block.
I then cut a pine block slightly smaller than the distance from the top of the 'L' bracket to the bottom of the ladder brace at the top of the soundhole. I cut a thin, gently tapered wood shim and drove it between the pine block which rested on the 'L' bracket, and the bottom of the brace. I tapped the shim a little further each week for about six weeks until the bottom of the fret board was just about even with the rest of the fretboard. The bracket, pine block and shim will, of course, remain in place. The strings were still a bit high, and any truss rod effect was maxed. The original bone saddle was as deep as it could go, so I belt-sanded off an eighth-inch of thickness from the forward part of that big, thick Guild bridge and reinstalled the saddle, the bottom of which I had also sanded down an eighth. I had to re-taper the bridge pin holes, but when everything went back together, the strings were just about right. The twist in the neck, which is down about 3/8 on the treble side from the nut, well, it just takes a slight wrist position change on lower barre chords. The guitar is now quite playable and the strings are about 1/8" at the fourteenth fret . Surprisingly, the tone was not affected by all this meddling. Hope this helps.