Since I can manage to drop the little Glow Plug Nuts even with the Fuel Injection Line Removed; I can say that I "need" to have the Fuel Injection Lines removed.
But, this also means not forgetting bleed the Air out of the Fuel Injection Lines after you put them back on.

Don't forget to Ream or otherwise clean the Carbon out of the Glow Plug Holes (a couple of threads on that).
I also put a Never-Seez type compound on the threads of the Glow Plug so they come out easier the next time.

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84 300D, 82 Volvo 244Gl Diesel