1984 300DT: throttle linkage ball socket replacement question.
 

I purchased new throttle linkage ball sockets for the 1984 300DT. Now, it is time to install them. I'm thinking of using either blue painters tape or blue thread locker to mark the exact position on the linkage threads so that I thread the new socket to the exact original position.

Does this sound like a reasonable plan of action?

It sounds like a good place to start. You may have to make an adjustment after installation to accommodate the new ball sockets. The old sockets may have been adjusted earlier to counteract any sloppiness, which would require a new adjustment for new sockets.

Sounds like it would work fine.

When I go my Car the linkages were the wrong lengths.

I used the measurements in the factory service manual and measured as in the attached picture in post #4 with the side of a ruler that is metric. That was back in 2007 and everything has been fine since that time.

http://www.peachparts.com/shopforum/diesel-discussion/406946-300td-throttle-linkage.html

Take pictures and make measurements. Record for a later date. If it is working fine now, then it will work fine later. You can adjust per the factory manual later if it there are measurements for your car. I have an 85 California model and have never been able to find a diagram or picture in a factory manual, let alone the linkage measurements.

Yours should either be the standard version of the 123.193 or the 1980 California version.

Here's the standard.
https://www.peachparts.com/shopforum/attachments/diesel-discussion/158730d1595782718-300td-throttle-linkage-30-300-p1.pdf

A cheap caliper helps too. It won't be long enough for some linkages, but for most it's very helpful.

FSM section 30-300 in the FSM on CD (and is the only listing for adjusgint the throttle linkage for my year and model), adjusting throttle linkage; length of regulating rod in mm (there is also 30-310 and 30-320)
The Paper Engine Manual is not as clear.
My 84 300D is the same as 123.193 which is at the top
3 rods from the firewall forward and the rod coming up from the bottom (which I have never touched).