I have been meaning to do a valve adjustment for the past month, and likewise, I had a spare set of injectors for my '84 300D that the local injection service place had cleaned and balanced for me. I wanted to swap them in because I have a nozzle that periodically sticks when the engine is hot. So I pulled the injectors, removed the valve cover gasket, and did them all at once. Diesel Giant's tutorials are excellent, by the way, and I picked up a set of his custom wrenches last year....makes it really easy.
Just FYI for anyone who hasn't heard this.... It's incredibly easy to turn the engine with the injectors out....No Compression! I used the power steering pump method, and it takes very little effort to turn it (always clockwise).
Started up and the idle was smooth. Response off the line improved. One bummer however. At least one of the unknown injectors has a similar nozzle issue. It only creeps up when hot, and only at idle. Tap the pedal and it goes away about 50% of the time.
So I have an extra set of heat shields, and might repeat the experiment later, but this time I think I'll just get a new set of Bosio nozzles and take out the guess work. I might give it a little time to see if it smooths out, or alternately if I can identify which cylinder might be the affected one, if I have the fortune of having it happen when I'm able to check, and swap out just that one with another spare.