There's a brown vacuum line going to the shut off diaphragm almost directly below the stop lever between the back of the injection pump and the oil filter housing. Disconnect that brown line at the stop diaphragm and put a long piece of rubber hose in its place. Suck on that hose with the engine running. If the diaphragm is good a couple of strong sucks should shut it off. (be aware that if the diaphragm is ruptured, you could suck oil) If it does, run the hose out the cowling, shut the hood, problem solved. Just suck on the hose when you need to shut if off.
Report back with the results.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13