Mounting a tonearm over a hole designed for Rega-style tonearm

One easy solution is to make a new arm board plate with threaded holes for the Triplanar mounting that attaches on top of the existing arm board. You can see what these types of things look like in my system pictures

The challenge will then be to attach it to the existing arm board using only the Rega hole without protruding above the surface level. I'd imagine a countersunk area around the hole allowing a nut to lie flush with the upper surface? I also suspect trying to fix the plate using only one large central bolt is not the most stable design

The other downside of this approach is that you are adding height to the mounting which may preclude achieving ideal VTA 

if if I was you I'd drill new holes in your existing board 😏

Another option is to use a tone arm compatible with that mount. I think Basis is one and Audiomods is another. There are probably others.

if I was you I'd drill new holes in your existing board 😏

+1
and if i want to switch back to the Rega-style tonearm, just add a one inches washer to cover those holes.
http://www.exercise-equipment-parts.com/1inch-chrome-flat--washer-for--foam-roller-pa1.html?gclid=Cj...

Dear @nrenter: Try to find out the Rega RB900 or 1000 or 600. These tonearms are very good performers and compete with those you name it.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.