I'm honestly not sure. I found the image during a GIS for "top shelf." I briefly considered shopping out the numbers because they irritated me, but right after that concluded I couldn't be arsed to do so.
because that is how jiml gets away with half the amount of parts.
for the srx circuit it works because a low impedance ground is not necessary.
i myself would not do this, i would do the usual 2 supplies tied together. It only took me about 1 hour to do that layout, so no biggie.
The right way to mount a TO-3 package is with a shoulder washer on the bottom and then using a ring connector to attach the case to the circuit. I am trying to do it another way. It will make more sense when I post some pictures