No, they are there so that the simulator will give you some way to report cathode and grid current. Neither are present in the test board. Generally, if there is a 1 ohm resistor in one of my schematics that was drawn in LTspice, its there so I can graph the current flow through that point.
I have never found the need for GNFB in a Single Ended Triode amp. The UNSET output stage has enough local feedback to generate triode like curves and output impedance, so no feedback is needed there either. This is of course greatly dependent on the speakers being used too. The SSE (Simple Single Ended) amp has provisions for cathode feedback around the output stage if desired. My preference was for a no feedback Triode wired EL34 for my Yamaha NS-10M Studio Monitors, and a Cathode FeedBack enabled KT88 or 6550 In UL for slapping the 15 inch Hawthorne Silver Iris Open Baffled speakers around with something loud like Pink Floyd's DSOTM.
Many of my push pull amps including the Simple Push Pull have the provisions for GNFB and it's gets used where needed, Including the 15 inch Silver Iris speakers.
Williamson's early work did predate my existence. I am in my early 70's. I started tinkering with tube stuff at a young age since discarded TV's and radios were readily available for free. There was no internet, or computers for that matter, and the only source of information was library books, DIY electronics magazines and the ham radio guy down the street from me. Solid state stuff was not too common except for the ubiquitous Japanese two transistor reflex circuit radio.
My first DIY amps were guitar amps. The first was a Fender Champ 5C1 clone with a schematic generated by tracing a genuine Fender Champ around 1962. The parts were obtained from dead octal tube radios. I did manage to clone a Vox Tone Bender germanium fuzz pedal with transistors from one of those two transistor radios. By high school I was designing and building primarily solid state stuff. Sometime around 1990 I traded my first car which was older than myself for a Scott 272 integrated HiFi amp and matching tuner. Once repaired it kicked the Carver and Phase Linear stuff right out of my stereo rack never to return. What do you think I built next? Yep, it was clone of that Scott. The seeds of Tubelab had been planted.
Those parts were used because there are models for them in LTspice. My board has an FQP1P50 in it for the P ch. Unfortunately, it has gone extinct. Crss is the spec that matters in a follower. The 9640 is 81 pF, the FQP1P50 is 8 pF The board has an NDF02N60Z in it for the N ch, also extinct. My guess is that a DN2540N5 will work in that spot and I have some.
The two letters after the "DN2540" specify the package. The N3 version is the TO-92. The N5 version is a TO-220, and the N8 is an SMD TO-243A. All have the same internal die chip.