Ok, I pulled the back of the cabinet off last night, wanted to see if I could remove that chunk of wood that covers part of the top left speaker where the Ampeg badge screws in. No dice. I'd have to remove the mesh and use a coping saw very carefully to not break it off past where the speaker screws in. I would eventually like to put some steel mesh in the front.
Once everyone is up and about today, I'll try my Les Paul and ES-335 through this rig. The power tubes are EL-34's and the preamp tubes appear to be stock Marshalls. I need to put some hours on this before I decide on new preamp tubes.