Just my thoughts... Three people in my shop did a FAIL using the procedure to replace the head seal and broke the distributor shaft on the pump head. We sell a used pump head for $400. Maybe you can get a head cheaper, but the best thing is to avoid the 'in place' repair.
It may lose the engine timing, but the time to bench the injection pump, it is much easier to see what you are doing and how to pull the pump back into place with the injection pump held verticle in a vise. That way, tightening the bolts back into place is obvious and less of a problem. Also, when removing the pump head, the shim, which you need to place between the drive shaft end and the pump shaft, can be held into place with a very small dot of wheel bearing grease. That will keep it from falling off when installing the pump head.
I wonder how many people have tried the youtube method shown and broke the pump head distributor shaft. Just this week, we got a call from someone who watched the video and failed exactly as I warn about... he broke the distributor shaft for the pump head. At this point, a different pump head may be found, but the shimming needs to be checked for proper stroke. We perform that service. and carry several of the spacing shims.
Yes, it requires a bit more time to reestablish engine timing. Yes, the procedure requires removal of the injection pump. But I have never broken a pump head with my method. And the 'fear factor' of dropping a shim is gone.
Once you have a good look at the internal operation of the pump and understand how simple much of it is (especially compared to a mechanical pump), you will be better able to judge the quality of the pump and it's maintenance needs.
Also, using my method, the chance for stray dirt entering the pump is gone. Washing the pump off in place can still leave stray dirt. A grain of sand can stop an injector from working and is another way you can compound your problems. It's best to have the pump head and body clean, inside and out for reassembly.
It's Thanksgiving. I wish everyone a great day. Enjoy the family and all the festivities.