Looking good! I can’t see your grounding scheme from the photos but isolating the power supply grounds from the input/preamp side will help keep the amp quiet. Run the grounds from the filter caps to the power supply side of the chassis, maybe to a lug on one of the power transformer mounting screws. And the preamp grounds together on the brass grounding plate or buss bar.
That’s exactly what I did! My friend/local amp tech explained that exact same technique. The amp is very quiet, and i’ve been gigging with it regularly. One thing I did was changing out the 25uF cathode bypass cap to a 4.7uf; still get a great boost in that position, but without the unnecessary “flab” of the 25uf at higher volumes.