Been a long time!
I have few notes, but I do have two hard-copy manuals; both have the same copyright tear (1997); penciled notes on the front pages indicate one of them is "second version with corrections."
In the original design (by John Tucker) the C4S draws its power from the 2A3 cathode (center pin of the 50-ohm hum pot) and is set for 8.6mA. The driver is a 5965 with the two sections paralleled. The 182-ohm unbypassed cathode resistor drops 1.56 volts; this combination gives about 100v at the driver plates, which are connected to the 2A3 grid (pin A3, connected to terminal 9). For some reason the voltage check at terminal 9 calls for 264 volts, but it should be 145 volts (the 2A3 filament pins A1 and A4 call out the correct 145 volts).
There was no grid stopper between the driver plate and the 2A3 grid, but I highly recommend adding one, right at the A3 socket lug.
As shown in the circuit diagram, the 2A3 operates at 250v plate to cathode. The cathode voltage should be 145 volts as specified in the voltage checks. In the earliest version, the cathode resistor was 2500 ohms, so the total current is 58mA through the resistor plus 8.6mA through the driver plates, plus whatever the C4S bias current is - probably around 2mA. Total 68.6, well over the tube's rating. Presumably for that reason, the revision switched to a 3000 ohm resistor to get about 58mA total, 48mA through the 3K resistor. That resistor then dissipates 7 watts and is rated 10 watts - there is not enough safety/reliability margin; it should be at least a 25-watt part. Note that, with 253 volts as you have measured across the 3K resistor, the current is 84mA and the resistor dissipates 21 watts!
After the original Afterglow, there was a period of rapid change and confusion, as the ParaGlow replaced the Afterglow, and the deYoung transformer became difficult to get so we transitioned to the Magnequest PGP8.1 which had significantly higher voltages. We also switched to using a single section of the 5965, and eventually the Russian 6N1P for the ParaGlow. My records and memory are insufficient for tracking that rather involved history.
I hope that's at least a little help.