Injection Pump Installation
 

Straightforwards scenario, I hope:

Bought a new injection pump over EBAY, looks straight off the assembly line, was supposedly never installed or used. Installed as per Mercedes manual guidelines. Part IDs match except new pump is CARB compliant (PES 5 MW 55/310 RS 16-1 instead of original PES 5 MW 55/320 RS 16).

Bled and primed fuel system, but am not getting any fuel from line #1. I am getting regular drips from the rest of the lines when I spin the engine over, but #1 remains dry.

Are there any further tests or checks I can perform, other than uninstalling and taking the pump in for a bench test? Would it help to backfill the pump on #1 (using an eyedropper and clean fuel) and retry?

This is on my 83 240D with 617-series 3.0L turbodiesel

No need to backfill the IP; you can just get on the primer pump and pump and pump.

Try removing the #1 Injector Hard Line down by the Fuel Injection Pump. Crank the engine and see if the fuel is spurting up from the delivery valve holder.
If not it is possible that the former owner left out the delivery valve spring (maybe during drip tube type timing).

No fuel with line removed. As far as I know, the pump has never been opened up/ worked on/ used prior to this. If the valve spring is missing, I suppose this means I have to remove the IP and have it bench calibrated? Or do the calibration/test bed warnings only apply to removing the whole plate assembly on top of the IP? (I'm looking at 7.1-210 in the Mercedes Manuals, if that helps..)

Look at the section of the Manual the deals with using the drip method of timing. To use the method you must remove the deliver valve holder (the part that the Injector Hard line threads onto). It will have flat sides on it likea a bolt dose or will need a special splined socket to remove it (I am not sure which you pump has ).
Take a look at the manual.
Also if you remove the Deliver Valve Holder you should replace the copper crush washer with a new one when you assemble it.