On my 84 & 85 300D's it has been fairly easy since I got a Craftsman ratcheting wrench set. They have a fine ratchet so you don't need to swing the wrench very far to get the next click. Works great on glow plugs too, swinging between the fuel injection tubes.

It is a little tricky working the shutoff valve past the oil filter housing. I suck in the stem with a vacuum pump and use the vacuum hose to help direct it. You must work it out of the pump, tilted towards the engine, then suck in the stem and rotate it. Of course, if it failed, you have to keep pumping to try to pull the stem in. I would never pull one before testing it with a hand pump.