cheek rest
I built one for a DCRA target rifle.  Except for avoiding the butt trap holes in a milsurp stock, the technique is the same.
- Drill two VERTICAL holes in the stock, stop before coming out the bottom.  My rods were 3/8" aluminum.  I made a some sort of cradle big enough to support the heavy end and that would fit on the drill press table.
- Bandsaw off the top 1 - 1 1/2  inches of the comb.  I cut HORIZONTALLY, then took another slice off at 45 degrees.  I wanted to not rest my face on an edge, but you could cut once on an angle.  I must have used a similar cradle, but I forget. 
- Drill two larger diameter holes on the exposed flat face of the butt, centered on the existing holes.  Mine were about 1" diameter, because I had some 1" aluminum bar stock.
- Epoxy glue the bar stock into the holes.  Make the top flush and pretty.  When cured tape the cut off comb onto the stock.
- Drill down through the same holes to make holes in the bar stock.
- Epoxy the rods in place in the comb.  Mask the bar stock to avoid leakages.
Use the butt and the bar stock as a jig to guarantee compatibility.
- Rebuild your comb.  I used epoxy and fibreglas fabric for strength.  You might do this simulataniously or separately.  I did it in two steps for control.
- Drill and tap for two thumb screws on the offside, through the wood and one side of the bar stock.
For a while I kept some sandpaper and soap in case the cheekrest tried to bind, but it was an easy job after a summer of matches.
I made up a bunch of veneer plywood spacers with holes for the rods, because I found the thumb screws would slip unexpectedly.  Experiment with the height for comfort and then keep that many shims in your shooting box.