It is difficult to see where the benefits are for the mechanical interfaces on the Tonearm using the methods suggested by the Tonearm Dealer you are in communication with.
For my TT setup, the arm sits on a tower (cylinder) adjacent to the platter. There is no plinth. The top of the platter is 57mm above the top of the tower. A disc, essentially the armboard, attaches to the top of the metal tower. The height of the armboard is machined to achieve the nominal distance from top of the armboard to platter as required for the selected tonearm. The dealer told me that this distance is nominally 30mm for the selected tonearm.
I fully agree that a change of, or addition of materials, in an assembly, at an interface where parts are fastened to each other within the assembly of the devices on the TT, will introduce a change to the Sonic Signature offered.
Exactly as explained to me by the dealer.
Whenever there is a junction between two different materials it creates a reflection boundary which in this case would be trial and error to learn of the impact of the reflected energy at the interface.
He described the sonic differences of various boards he has machined for customers and his own setup. I have no desire to painstakingly try many armboards to find the ideal material for me. I can leverage off his knowledge and experience to provide advice to me, the customer, as to what material will work with my system and sonic priorities.
He said I could try the existing metal disc I have, with or without a thin wood shim, and see how that works out. Based on all he shared with me, I had no desire to do this. And he said that metal on metal will result in an exaggerated top end with added "detail" which does not appeal to me.
Ultimately he suggested one of the exotic hardwoods for my setup. He said that after I give this a serious listen, and if something is "not quite right", we can discuss further; he would send me a different board to try. Customer service does not get any better! The end result with what he sends to me in a week will be far beyond what I have ever had on a TT.