Thanks Simon.
I purchased an Allparts SG wiring kit which came with the large pots so recessing them might be a bigger job. I will assess how things are going as I carefully route out the cavity.
My measurements today indicated that the 3/8" shaft is just long enough. Anyway I can get longer shaft ones if necessary.
5mm of this heavy Qld mahogany would me much stronger than ply.
Thanks again for your advice.