I have my 84 300D Turbo engine out of the car and am preparing to install it in a 82 240D 4 speed. What should I do to the engine as far as maintenance / upgrade while its's out of the car? Is there anything regarding the turbo that I should do? I'm using new motor mounts, new exhaust, new glow plugs, and a new clutch / pressure plate - is there anything else?

I would pull the pan and put new rod bearings at least... and front and rear crank seals..... new throw out bearing and pilot bearing....clean the oil pan ....take the freeze plugs out and use a high pressure nozzel ( 90 degree ) to blow out the water jacket as best you can.. run water until it is clear...check for chain elongation and replace if needed... or use offset key to correct for elongation if that will fix it...renew chain slides and spring in oil bypass....and take chain tensioner apart and clean it... renew if possible
Put new turbo downtube gaskets in ... I think you need to have the pan off so this is the perfect time for that as you go back together...
You are going to have the perfect car... so if you have the money you might consider a new oil pump while you have the pan off...and water pump..
The turbo's on these cars are amazingly long lived.... they run much cooler than gas engines...
I suggest you mount the engine on a sturdy engine stand which will allow you to rotate it safely....will really help on the water jacket cleaning...set the valves while it is out.. much easier to access...