Hi Mike the injector pump is a very simple device and very robustly built, provided the rack moves freely it can be rebuilt and reused. The originals have the advantage of having a hole drilled at both ends of the rack, this is to accommodate the starting pawl which sets the fuel delivery to maximum for cold starting. The Mico/Bosch replacements do not have this. Replacement elements are available for these pumps.
The original fuel injector is also very robust and can be rebuilt, provided it has not rusted solid. New injector nozzles are available but I would recommend giving the old one a very good clean and lapping the seal with a little Brasso metal polish and seeing how it goes. One thing to be aware of is that there is a 5 micron fuel filter built into the fuel inlet pipe, hidden in the 2 inch long threaded pipe connected to the injector. The inside of that pipe is ground to a very fine tolerance and has a fluted insert in it that is also very finely ground. If these are rusted then no fuel will pass and it will never start. It is OK to knock out the internal fluted insert and chuck it in the bin if it is damaged, I don`t recommend it but provided you are fastidious about keeping your fuel filters clean, it wont cause a problem.
BruceM is absolutely right about the pop pressure not being critical, somewhere I have the original instructions on how to field set that pressure in an emergency. I would recommend you rebuild the injector and then take it to you local diesel engineer to have the pressure set, should be a five minute job and cost very little. Failing that please send it to me and I will set it and send it back to you free of charge.
Bob