A few other thoughts as long as you are doing a rebuild. None of these are expensive.
(1) Replacing all the resistors with metal film is a good idea. The carbon-composite resistors will likely have drifted, and they have poor properties in any event.
(2) Adding an inrush limiter can help reduce stress on the rectifier and transformer when the filter capacitors are empty and thus appear like a dead short. The inrush limiter to the heaters reduces the stress.
(3) Adding solid-state diodes to the 6X4 will greatly reduce the PIV stress and prolong the tube's lifespan. You'll still get the gradual B+ delay, but the rectifiers will take the AC stress, not the tube.
(4) At the transformer's secondaries, separately fuse the heaters and the B+. On startup the heater current is many times normal load, so the primary fuse is geared for that, not a B+ short. If the 6X4 goes it will short and take out the transformer. Small fuses (50 to 80 mA) exist and these may protect the transformer in the event of such an overload because of rectifier failure. Yes, the tubes tend to be reliable, but if (when) it shorts the transformer will likely melt before the fuse blows. Replacement transformers for old gear can be hard to find and expensive.
(5) After you clean the potentiometer add some silicone grease as a lubricant. It was built with this when it was new and it keeps the wiper from wearing away the resistive element.
(6) Change the bulb to an LED and this removes some of the heater load. Also removes some of the heat needlessly generated.
(7) Polish the chassis with Simichrome or Mother's Mag and Aluminum polish. It will look better than new when you're finished.
Good luck with the rebuild.
Edit: added LED.