As per the ground reference: I did it in 2 or 3 units, welding the "grounds"
of the circuits to the points of the strips that were in turn bolted to the
frame plate. I do not understand why a bus wire should be a better "zero"
(ie. lower internal resistance) than a 3 mm thick plate, 12" wide by 16"
deep. (Obviously the abovementioned units were all power amps, I never did
this with phono stages..)


I would avoid passing heavy currents thru the chassis, like
heater currents (could create some hum as some "grounds" would
have some 60Hz voltage developed on it due to the chassis
resistance (low, but not zero). I usually do "star" grounds
where things like the ground return of the power transformer,
negative side of filter caps, and cathode resistors for the
output tubes meet. It's much easier to manage current flow
paths with separate wires than trying to predict the paths
currents would take thru a chassis. Some production amps
did use the chassis, but that's after an iteration or two
in the lab by experienced people. And they probably did
star the high currents and used the chassis for small currents.