Changing the fuel filters is pretty easy. Fill the big filter with purge, or diesel, or ATF or something before reinstalling it.
You should be able to test your fuel flow by disconnecting the return hose and sticking it in a bottle to see how much fuel it spews out.

There are other issues with the 3.5 diesel which, if you don't already know about them, you probably don't want to learn. I don't know how much those problems effect starting.

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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