Those are very informative pictures, thank you for sharing them. As you know dark color plastic guides can indicate brittle parts triggered by heat and age. Are these parts visible anywhere without disassembly of the whole front of the engine? Did you complete this job with the engine in the car, following a procedure I can find here? Thank you for your insights.

 

You only need to change the secondary tensioners , it just requires moving one cam each side, pretty straight forward job, no special tools needed.