Hello, I am going through the same thing, I bought a Rek O kut B-12GH and will build a plinth. Ideally, I would like to find an arm that would be a drop in replacement, I need to go to vinyl.engine before I start enlarging the existing hole. I have read conflicting reports as to what is best when it comes to mounting the arm, top plate mounting vs plinth mounting. It has been suggested that the table can be mounted in the plinth by turning the table so the top of the top plate is now located on the side where the arm is usually located and the arm is then easily mounted in the plinth, hope that makes sense. My table came with a ROK arm but it had some problems and the bearings are really sloppy. I may go for a Rega and enlarge the existing hole to get the correct spindle to bearing dimensions, plus the arm is cheap and can be upgraded. One of the important things when building one of these tables is to get the Idler wheel rebuilt by Ed Crocket at Vintage Electonics, total cost is approx. $30.00. I want to build up the table first and listen to it then have the Idler wheel rebuilt to see what the improvement is. What materials are you going to use for the plinth? Another site with good info is Roktips. Good luck.
Phill