Tonearm mount to the plinth vs arm board vs rotating arm board vs isolated tower

For practical reason this type of Steve Dobbins plinth for Garrard 301 is universal for different tonearms if you're going to use many.
Same construction in Stereophile article

Aesthetically Artisan Fidelity 301 is the best (imo), but you need many armboard to swap tonearms.

Well, I know Steve Dobbins. I have met him face to face and have had extended conversations with him about optimization of the venerable Garrard 301. Steve will tell you that the swiveling arm board is a compromise and is not optimum. It is a useful convenience feature. A very useful and very convenient feature but still a compromise. For optimum performance, he advocates mounting the tonearm directly to the plinth. No replaceable cut-outs, no extensions, fixed or rotating. Why should this be surprising when extensions resemble diving boards?
Everything needs to be kept in perspective. The Garrard 301 is not the ultimate in terms of being quiet or in terms of speed accuracy. Instead, it has it's own sound, a very good one. In light of that, one should not sweat bullets about having or eschewing a rotating arm board. They are clever and indispensable for those that want to use lots of different arms. The compromise in overall SQ is likely negligible. I would argue that it is only when using the very finest MC cartridges with the 301/401 that one should avoid any otherwise avoidable compromises. 

Steve will tell you that the swiveling arm board is a compromise and is not optimum. It is a useful convenience feature. A very useful and very convenient feature but still a compromise. For optimum performance, he advocates mounting the tonearm directly to the plinth. No replaceable cut-outs, no extensions, fixed or rotating

For Garrard or for Direct Drive too ? 
Such plinth is easy to made if we already have one tonearm to mount. 

We were discussing the Garrard 301 at the Axpona 2019 room featuring his turntable, a 301 on a Dobbins plinth with a Reed arm and a top of the line VdH cartridge and Magico speakers. I don't recall the electronics in that room. The room sponsor was Van den Hul's former distributor who has since then been replaced with VPI. 
My opinion though, fwiw, would not change with any type of drive system. 

I see, the goal of Reed is that a mounting hole is not needed under this tonearm, it can be screwed to the flat surface with 3 mounting screws from the top.

Here is the engineering principle that must be observed when designing a plinth for a turntable:

The plinth must be as rigid and as acoustically dead (damped) as possible. The mounting of the platter bearing in the plinth will be thus coupled as rigidly as possible to the mounting of the tonearm. If it is not, any vibration at all can be interpreted by the pickup (arm and cartridge) as a coloration.

IOW, if the arm and surface of the platter are able to vibrate at all, if they are always in the same plane of vibration, the pickup will not be able to pickup noise or coloration on that account. So a separate arm tower is a violation of this principle and induces coloration;  the same is true of a separate arm board. If the arm board employs damping and the plinth does not you'll get a coloration. It all simply has to be as rigid as possible and damped.