"Anyway, next step, ... is to pull apart the fuel distributor,"

If "pull apart" means separate the 2 halves of the FD, then the next step after that will be to toss it in the scrap metal bin. They can't be resealed once separated. But you could remove it to see if the control plunger is free to move up and down to follow the airflow plate movement.

But that's where 15-20 minutes with the gauge would tell you if you need to spend that 2+ hours of time and effort on the FD or not. What is your time worth?

Phil and Dave's tip on the Frequency Valve is a good one, now that we know you have one. You can check it for "buzzing" with the engine off by unclipping the Lambda relay on the fender rail to turn it upside down. Then use a jumper to "back-probe" +12V from the battery onto the Blue wire terminal at the (still connected) relay harness plug. The relay should "pick" immediately and make the Frequency Valve buzz noticeably.

EDITed in at 9:49 EDT:

"...jumpered 5 and 7 and the pumps appeared to run."
You can also test each pump separately by removing fuse 5, then jumper the +12V to the LEFT fuse 5 contact to run the Main pump or to the RIGHT contact to run the Tank pump.

BTW, does the car have 12 fuses or 16 (like the '79 and later 240's?
If it has 16 fuses, it may be that the wiring is basically like the '79.
If 12, I'll have to refer to an old Clymer manual for any more tips.




--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.