The peghead area has to be made quite thin to allow mounting the tuners the conventional way (i.e. from the back of the peghead). Standard tuners can be mounted on 1/2" to 5/8"(13-16mm)-thick pegheads.
Choose one side on one end as the face side, measure 5-1/2" (140mm) back from the end and pencil line A parallel to the end across the plank. Mark this line also on the sides of the plank. Adjust a marking gauge to 19/32" (15mm) and mark the peghead thickness up to line A on both sides and the front of the plank.
Put the plank face down on the bench and measure 7" (180mm) back from the end of the guitar plank. Draw line B parallel to the end all the way round the plank. Mark a round transition from the peghead to the body of the guitar on both sides. See if you can find a circular object with a diameter of 4" to 4-3/4" (100 to 120mm) that can be used as a template; a compact disk, for example, would be fine. I used a plastic cup with a diameter of approximately 110mm. Finally, draw a line at a distance of about 1/32" (1mm) from line C (i.e., 5/8" (16mm) under the face-surface of the peghead). This will be the line for the saw guide to follow.