If this happed to what would be the least confusing would be to just resign Myself to the fact that the Fuel Injection Pump needs to be pulled out.
This also means You will not need to worry about the mark you painted; just use the Engine Timing Marks.

Once the Fuel Injection Pump is out you only need to line the Crankshaft Damper to OT and line up the and get the Timing Chain and Gear back on the Camshaft with the Timing Mark Behind the Gear and the Camshaft Bearing Tower markline up.

I assume when you do that you apply a counter clockwise force on the Camshaft Gear + Chain before you slide it on so that you are pulling the Chain tight from the Cranksaft Gear and the Timer Gear. Because the Timing Chain Tensioner is not on yet.

If you have a Turbo Model the Timing Chain Plunger Piston needs to be reset; pulled out and re-inserted; as it only goes one way; and it needs to be inserted from the opposite end.
Of course the Timing Chain Tensioner Rail goes in before the Tesioner does.

If you are reusing the Timing Chain I would not expect that when the Camshaft Gear/Bearing Tower are lined up that it is going to be lined up with OT on the Damper. I would expect it to line up somewhere after Ot (Top Dead Center).

After the Timing Chain issue is sorted out then you can deal with the Fuel Injection Pump Timing.

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84 300D, 82 Volvo 244Gl Diesel