NOTE: Do this only in an emergency if your pump Element O-ring is leaking and it looks like you are going to have to send it off to a shop or buy a rebuilt pump.
If you have a good pump with no problems and decide to go exploring that is on you.

If you decided to pull the Elements (one at a time) the best place to scribe a line is on the Engine Side of the Fuel Injection Pump; as that is the place that has the flattest surfaces.

The Element Flange is hardened Steel so you will need a Tungsten Carbide Scribe.

Us a Ruler and scribe the line Straight; not so easy to do.

After that take a picture of the Scribed area so that you can match it up exactly the way it came out.

Don't lose the Shims that go under the Element Flange and remember which side the shim came from.

I have an extra IP and decided to remove an Element.
So it is already been scribed. I removed the 13mm Nuts and washers. You can see the Fuel adjustment slots; this is why you are not supposed to be doing this except in an emergency.
I decided to take a measurement as a back up.

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84 300D, 82 Volvo 244Gl Diesel