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1965 Silvertone Harmony model S1478
With Original Fibreboard Case
~ Page 39;  Detailing Neck Screw Holes;
And Shim to match the bridge, fretboard and pickup height geometry ~
The correct neck angle is determined by several factors:

(1) The median height of the bridge height adjustment so the bridge can be adjusted both upward and downward, and;

(2) The best string height above the pickups that do not adjust up & down, and;

(3) The string height action on the fretboard.

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(1 and 2): The median height of the bridge height adjustment and string height above pickup:
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(2 and 3). The best string height above the pickups and, the string action height above the fretboard:

Tilting the rear end of the neck heel upward with the shim will bring the fretboard closer to the strings while thus also tilting the headstock downward which will lower the strings toward the fretboard.  A good rule of thumb is that the shim's rearward / thickest end should be half the thickness of the distance needed to be reduced at the last fret.
(3). Playing action string height measurement:  Mic'ing the additional height needed by a neck pocket shim reveals .150"  distance the shim will need to provide.  Approximately half of that will come from the shim raising the back of the neck heel, while the other half by the subsequent lowering of the nut relative to the body in the new / correct neck angle:
Four layers (for durability) of masking tape is pressed into the neck pocket, tightly into the corners gently using the end of a round toothpick as each layer of masking tape is applied.  A lead pencil is then used to both again press the tape into the corners and mark where the tape should be cut for an exacting template of the neck pocket.  This template will be applied to the shim wood as a pattern to cut and sand around.  Write the shim's orientation into the pocket so there will be no mistakes in the fabrication & installing process.
The template applied to the shim wood.  Notice that the screws were installed so that just their tips stick slightly out of their holes to mark the center of the holes onto the template when it's still in the neck pocket:
Here you can see the Dremel wheel grinding saw working OUTSIDE the template, leaving plenty of meat to sand down.  You can always sand down to the template but will have to start all over (for a good job) if you cut or sand into the template: