Click on any of these images for a closer look.

First find the exact position you want, then put a couple drops of "crazy glue" through the screw holes.  In a couple minutes, the bases will be held frimly enough to make a nice scribe line.

 

 

 

A sharp twist will remove the swivel, you now have that line as a guide.  I use a small router to deepen the mortise. 

 

 

 

Inletted to final depth...now drill for the screws and install, be sure to bring the slots n/s. 

 

 

 

 Shape/polish to match contour of stock.