I am betting on a small Air Leak. Changing the Fuel Inlet hoses with 5/16 Fuel Hose from a regular auto parts store (it is rated for Diesel) is cheap trouble shooting. (Do you still have the Old Style Hand Primer?)

When you had the Fuel Pressure Relief/Overflow Valve a part was the Ball Bearing rusted on any part of the surface. If it is It may not always be sealing.

There could be some valve not sealing well issues in the Fuel Supply/Lift Pump.

I do not know what TDC offset is but your pointer is pointing to about 4 degrees of late timing. But, that is nothing that would cause an intermittent issue.
Also in the Manual whe you aline the Camshaft when you build the Engine it just has to set it at TDC, no mention of any sort of off set.

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84 300D, 82 Volvo 244Gl Diesel