Did you try a different speaker and cord first?
Turn the amp on, turn the reverb up midway, they rock the amp to crash the reverb springs. Does that come out loud or is it also diminished?
Your screens come from ultralinear taps on the OT and so naturally have a slightly higher voltage.
And you don;t really have 85v on your PI grids, that is meter loading. I am sure the voltages are fine, but if you want to know what is on those grids, instead of measuring to ground, measure from the cathode direct to grid. Then the volt or two you get you can subtract from the cathode voltage to get the grid voltage. The grid voltage there should be about the same as the voltage at the bottom end of that 470 ohm cathode resistor.