The book says: The shock pistons are 46 mm.
I just measured the outside diameter of them at 53 mm.
Therefore the walls of the shock tubes are 3.5mm or~9/64ths.
A 4-40 screw is 7/64 or 2.7mm.
If you drill axially into the tube and tap it for a 4-40 screw you should leave~.8 mm or 1/32 on each side. Assuming "balls on accuracy”
Can you stand it!