I installed a turbo hood liner in my 89 240 with no problem. I had to put new holes in the hood liner and bought a couple of extra plastic pins (or whatever you call them) to attach to the 86+ hood. If an 86+ owner is looking for an exact fit, the 1993 "240 classic" had a hood liner. The turbo hood liner made a big difference in my opinion. Still looking for those under dash pads from a 240 diesel.

I added some 1/4" thick rubber tape from Home Depot to the inside of the window fram. It helped a bit with wind noise but I'm not sure it was worth the effort.

A few changes under the hood made a huge difference in noise. First I replaced the clutch fan with an electric fan from a 940. Gained a little bit of power, a little bit of fuel economy and a lot of quiet. The fan only runs when the car comes to a complete stop for more than 30 seconds controlled by the thermoswitch. You would be amazed how much noise (woosh) comes from the clutch fan and not from the engine itself.

Second I cut down the number of belts under the hood from 4 to 2. Having 2 belts around the water pump and alternator creates a lot of noise. Inevitably one belt will wear out and streatch faster than the other. When this happend the belt with the least tension begins to make noise. Since I no longer have the clutch fan being driven by the water pump, I only need one belt.
My AC has been dead for about a year now with no plan to fix it in the near future. I removed the chain of belts from the crank to the AC to the PS pump and just ran one belt between the crank, water pump and PS pump. The belt is 47.5" long. This way I still have a back up for the water pump should one of the belt fail. I'll be removing the AC compressor and condensor in the near future.
Right I can't even hear the engine idle at a stop light. Its almost as quiet as my 960.
Cheers
Justin