Good Morning, Natron,
Could the triangular items be intended as reinforcement for the upper corners of the enlarger frame? Somewhere in the vague recesses of my memory, I seem to see a picture of a 23C with such reinforcing/strengthening corners in place.
ElrodCod has a good point about using only top-quality enlarging lenses. The El-Nikkor you have is one of those; it's most unfortunate that yours has the fungus problem. Unless the market has taken a major turn in recent weeks, however, you should be able to buy a 2.8 50mm El-Nikkor for a very reasonable price on E-Bay. It's been a buyer's market there for darkroom equipment for some time now.