FYI, my only "concern" at this point is normally the voltages on V2 and the voltage on V6 are about equal.
The Heathkit schematic shows these all at 280V. From above, after adjusting the pots to get equal voltages, you were getting about 320V on V2 and 225V on V6. So V2 high and V2 low and they are not equal.
Need to check if the drifted resistors values are contributing to this.
Maybe measure the voltages:
- "B+b" marked on the schematic, where R32 (1k) and R26 (1K) join
- "B+c" marked on the schematic, where R52 (27k) and R53 (27k) join.
- While you are there, measure "B+a+, at any point on the wire connecting R56, R31, R45 etc.