I know this an old topic...but Tonearm for Garrard 301 :)

What cartridge are you considering?  The important match is between the cartridge and the arm.  A local dealer does a lot of refurbishing of 301, 401 and Thorens 124 tables.  He primarily used Ortofon tonearms and Koetsu cartridges. Koetsu went out of business so I don't know what cartridge he will now be recommending, and Ortofon sourced its tonearms from Jelco which also went out of business.  This dealer said that the new source of Ortofon arms (also Japanese) is quite good, but, I don't know what cartridge he will be recommending when his stock of Koetsus runs dry.

Oh looks like your arm board is predrilled for the SME type base. Also looks very nice, and lots of room for the arm/arm wire etc. Should be a great sounding table.

Not sure about a tonearm that is not connected tt the plinth, one bump and your dragging out your alignment protractor. but a very interesting concept, if works well maybe an easier way to add a second arm to my table. 

Audio Creative Groovemaster?  Perfect for SPUs.

I am an advocate of the rigidly coupled design for a TT, with Hard Interfaces at the critical mechanical interfaces on the Plinth / Chassis.

I have used this method for the best part of 30 years when I weaned off Belt Drive TT's, moving to Idler Drive TT's and eventually having a 401 in a '9 Stone in Weight'  Granite Monolith Plinth > SME IV. This interest in Idler Drives evolved to Platter Spindle Bearing being overhauled/redesigned, through to a PTP Solid Nine with a bespoke design Platter Spindle Bearing, all mounted as a rigidly coupled design. 

Today I use DD TT's as a rigidly coupled design.

I have in the past developed an interest to learn about the influences of a variety of Tonearm > Cart's (LOMC - HOMC - MM ) in use on the Main TT.

To make this an easier to create experience I designed a Standalone Tonearm Pod, which had a design incorporated to toy with damping and enable different interfaces between the Pod Mounting Plate and TA. I did not use this method in the end, other experiences changed my direction.

An individual who has a system I am very very familiar with, has a SP10R > Glanz MH1200 > Miyajima . With the TA mounted on a Standalone Pod.

I have failed to detect anything that is detractor when experiencing the SP10R that could be associated with using a TA on a Pod.

With TT / Pod both sharing the same Sub-Plinth as a mounting platform there is an improved coupling in place to having different surfaces for each part to be interfaced.

If the Sub-Plinth is specifically selected for being a very stable material with attractive Damping and Dissipation properties, this can easily be a better marriage for parts to interface than what many TT Designs are able to create. 

Keeping an open mind, and having simplistic options in place for creating new experiences when curiosity takes over is key to creating continuous opportunities to learn.

A sweet spot has been found for some, just through an alternate Headshell Material or Platter Mat Material being tried out.