I'm not completely sure that that stamping really does indicate that the head was cast in 1984, but if so, then that would also explain the absence of the "D24T" stamping on the head. The stamping is quite obvious on a small horizontal surface at the front of the head, on the driver's side, above the power steering bracket, just behind the inner timing belt cover. The stamping, however, was only present on MY83 and MY84 cars, and was absent from MY85 onward. Since MY85 engines were built in 1984, it stands to reason that if your head's stamping does indicate that it was cast in 1984, it was probably installed into a MY85 car and as such did not have the stamping. My guess is that your 1983 car had a 1985+ engine installed, and additionally for some reason got a NA injection pump too. It's always interesting to try to figure out what happened to these cars over the course of their maintenance history... so many gorillas butchered them and put incorrect parts on incorrectly over the years, that it is often a guessing game to figure out why an engine is equipped with the components it is.
The stamping is just visible in this photograph of my 1984 760 TD's engine. The photograph is one that I just happened to have on hand, sorry it is not focused on the area where the stamping is, but if you look close you can see it in the location I described in the paragraph above.
