I get your point on guide rails, but if you would do this and rattling stops then it should be fine i guess, until it starts rattling again.
At least you can do it in 2-3 hours of work, preparation/wrap-up included.

What is the current mileage on your car?
Mine it is only 110k but i can hear a small rattle on the right side of the engine, valve cover. (when looking from it from the front)
Will try the tensioner and then a chain swap.
Taking the whole engine apart only for timing at only 110k, i would rather let it blow up and deal with it then.
I doubt that it will break anytime soon.

I am only hearing the noise when idle. As soon as i rev it up a bit any rattling disappears. Maybe due to increase oil pressure or chain lack of oscillation under load or at different rpm.

Also, it could be the oil-pump spring tensioner but then it won't be quiet when revved.