Drew,
The top plate is 10" x 12" and the alder stock is about 13/16 thick, and there is a rabbet along the inside edge that is approx 3/16" wide and about 1/8" deep. That said, I'd wait until I have the plate in hand to make sure everything will fit nicely. BTW, don't make the plate fit too tightly in the base as there will be some thermal expansion of the plate.
You may also want to adjust the depth of the rabbet for different appearances -- I tend to prefer that my plates sit just a bit below the edge of the wood and others prefer it to sit a bit proud of the wood.
HTH,
Jim
Jim Rebman -- recovering audiophile
Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).
s.e.x. 2.1 under construction. Want list: Stereomour II
All ICs homemade (speaker and power next)