Pull the grounding lug of the two volume pots right down and solder them to the pot's shell.
The first two filter caps (or all three) negative leads can be connected.
Main thing is to bring the red/yellow center tap from your high voltage secondary right to the eyelet of the negative lead on the first filter cap... you can then run a ground wire from there to the chassis.. like a PT mounting bolt with a star washer lug.
The preamp stages should be ground well away from that point... ground the 12AY7's 820 ohm resistor and it's bypass cap, of the 1st preamp tube to any of the grounded lugs of the input jacks.
Ground the 12AX7, second preamp stage's 1500 ohm resistor and it's bypass cap with the grounded 56K resistor, close to the tone pot ground or at the negative lead of the third filter cap.... and don't forget to ground the 220K power tube grid load resistors to the negative lead of the third and final filter cap's negative lead too.
If you have a 6.3vac filament transformer with a center tap... bring that wire...(usually green with yellow stripe) ...
over to the positive end of the power tube's cathode biasing resistor or right at the first 6V6 tube socket lug 8.
If you don't have a center tap, use two 100ohm to 150ohm 1/2w resistors across the two 6.3vac leads, to make a virtual center tap, and connect the junction of those two resistors at the cathodes of the power tubes.
Should be pretty quiet.