Reed 3P armboard mounting

Think of it this way btw-the specified P-S is meant to permit the user to align the widest variation of cartridges in terms of mounting screws to stylus distance. 

Proof lies in the modern SME methodology. With modern SME arms there are no headshell slots-the cartridge can only be mounted in one fixed position and the solution is to slide the tonearm mount closer or further back-CHANGING the P-S! There is an invaluable lesson to be learned by the SME method of obtaining alignment.

Nothing new here, Luxman made it for ALL tonearms on PD-444 in the 70’s with metal armboards on the rail (can be moved to the left or to the right to change PS distance).

Nowadays Feickert did almost the same on his turntable.

*New SME tonearms are the ugliest on the planet in my opinion.

Aesthetics are so so personal. For moi, I am not a huge fan of that gaping void on the Feickert and all similarly designed decks to allow for changing the P-S. Is it clever? Hell yes. The pivoting arm board leaf used by Woodsong does the same thing for me-nothing. In fact, I firmly believe that the pivoting arm board leaf in fact compromises sound by promoting unwanted vibration. At least the void on the top surface inherent in the SME and Feickert designs don't constitute an engineering compromise. 

Dr. Feickert just copied today what was made 45 years ago in Japan by Luxman (much better design in my opinion). 

Pivoting gunmetal armboards also designed way back by Micro Seiki as far as I know, and I think it's worst that Luxman metal armboards on the rail, because Luxman armboard can be fixed properly.  

Slotted head shells and adjustable bases are supplied to accommodate various cartridges. The idea being to maintain the proper overhang dictated by the effective length and offset of the arm. The pivot to spindle spec is chosen to get you in the ball park. The cartridges geometry will dictate the exact location.
Using threaded inserts in wood is fine in this context if done right. Wood is soft. The threads of the insert will displace the wood upwards causing a dimple. The tonearm will then not lay flat on the arm board. You have to counter sink them then plane the surface flat. What you are doing is converting a machine screw to a wood screw.
Running machine screws through the arm board and bolting the tonearm down is a bad idea. Again, wood is soft and will expand and contract with humidity and the seasons. Through bolts will always loosen even if you use washers. Of course this is not true for metal and synthetic materials. These you can drill and tap. Best for wood is wood screws. Just size them appropriately and predrill the holes. As fsonic relates the exact pivot to spindle distance is not critical but if you get to far off you may not be able to adjust the arm for certain cartridges.