Tonearm mounting differences Graham vs.Tri-Planar.

Yes, the Tri-Planar has adjustable high as well.
I am not sure if the same board would work since highs are different.
At worst case I would order the custom arm board.

Rokokono,

The same height mounting board will work for both arms. I've seen it done on more than one table.

The hole drilling patterns are quite different however, as are the mounting distances from the TT spindle. My suggestion would be to have a board dedicated to each arm.

Here is a picture from both Arms

Graham Phantom / Triplanar
Above the Armboard they are more or less the same, the main difference here is, the Triplanar is a "on Board" mount, the Graham Board needs a hole because the Arm shaft and the Din Connector is below it (you need some space).
Graham Phantom

Dougdeacon and Syntax,
Thank you so much for your advice. Now is clear, I will keep the same arm board and re-drill it for the Tri-Planar.
Now I need to find one somewhere.

Dougdeacon, based on your previous post and experience, would you confirm that for ZYX Airy 3 cartridge the Tri-Planar would be one of the best options among others.

One of the best? At its price point I'd say yes.

Syntax has compared Tri-P vs. Graham Phantom using a UNIverse. I believe he prefers the Phantom with that cartridge. That's a bit costlier though, as you have to buy a tonearm cable.

Schroeder arms are also good with Airy 3. Softer bass than a Tri-P but quiet and with a low sound floor, which helps the Airy 3. It's a lively cartridge and likes a quiet arm.

The Durand Talea is the best tonearm I've personally heard (with ZYX UNIverse or Ortofon A-90). I've no doubt it would be exceptional with an Airy 3 also, it's the quietest tonearm I've never heard but sacrifices nothing in terms of solidity. Quite a bit costlier than Tri-P however.