If the Fuel Injection Pump is out of the Engine install the Timing/Locking Pin and rotate the Fuel Injection Pump Camshaft unit the Timing/Locking Pin lockes the Fuel Injection Pump Camshaft in place.

Rotate your Engine Crank Shaft in the direction of rotation past TDC on the Compression Stroke to what ever the degrees (about 14-15 ATDC; you will need to look up the spec for your Engine ) are ATDC (After Top Dead Center past TDC on the Compression Stroke) and install the Fuel Injection Pump and bolt it down and remove the Timing/Locking Pin.
All of the above should be detailed in your Manual.

Before you start rotating the Engine; even by hand you ought to Oil up the Chains and Chain Guide and the Camshaft Lobes. If not then before you assemble the Covers over those items.
You especially don't want a Dry Chain running over the Shoe on the Timing Chain Tensioner/Guide Rail.

The Engine looks very dry; you use any sort of Assembly Lube on the Engine and Camshaft Bearings? At least pre-lube with Oil.

Some of the methods of pumping Oil into the Engine to pre-lube may not gett Oil to the Timing and Oil Pump Chains.

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84 300D, 82 Volvo 244Gl Diesel