It's definitely not filtering issues with clogged filters. I had those in the past and know how they feel like. The owners of all cars either use the same grease as me or are pretty competent filterers by now.

Since you brought up filtering: the grease I use is from a Wendy's restaurant and partially hydrogenated. Possible that the IP is all clogged up from waxes in the oil.

I also forgot to mention two things about the car:
it gets fuel to all injectors although timing is unknown
it won't start on starting fluid (if I am doing it right, of course. It's a first for me)
camshaft is turning as confirmed by looking into oil filler neck while cranking.

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84 300SD with Greasecar vegetable oil kit. Boston, MA