First light
Measure the HT on the 800mA fuse and make sure it's under 200V.
Swapping the drives to the tube guns around is a normal diagnostic practice.
Yes, the G8 is a live chassis set!
If I recall correctly, the red green and blue A1 controls are at the bottom of the convergence panel at the front of the set behind the speaker grille. They work like individual brightness controls,