Which oil viscosity to use is dependent upon the ambient temps where the car is used. I generally used 15W-40.

It is important to use C rated diesel oils that have soot carrying capacity e.g. Delo, Rotella, DelVac and ZDDP/zinc for the sliding surface flat tappet cams. Motorcraft diesel oil advertises 1000 ppm on their bottle, that's a decent amount.

Good luck!!!

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