I have a number of items I want to take care of on my 1983 300SD but have to do it over the next couple of months.

In what order should I do them in relation to the most important. The car is running great. I am starting to hear some nailing in first gear only. I am getting about 29 MPG. with 266,000 miles on the car. I have had the car for about 60,000 miles and the previous owner had the car for 4 years with no real work done on it. Here is what I would like to do

1) valve adjustment - Has not been done as of yet.
2) timing chain - probably the original one
3) injectors - could be the originals
4) Deisel purge - Has never been done to my knowledge

I run about 40,000 miles per year with 90% being on the highway running the car 1 to 2 hours straight per trip.