When I did mine I of course left the Cmanshaft n place and removed the Rocker arms and likely some Glow Plugs so the engine would turn easy.

When Number One is at top dead center on the compression stroke the camshaft lobes for the number one cylinder are in kind of a "V" configuration pointing upwards.
When you rotate the Engine to get to the next one same upwards "V" configuration is what you want to see on the next Cylinder you intend to do next and it will be at or extremely close to TDC.

I don't recall having any issues compressing the valve springs and upper plate to get the valve stem nuts on. I also don't recall what I did to do that. However, the Camshaft is there and you can get something between the shaft and the top spring retainer so you lever it down and compress the spring.

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84 300D, 82 Volvo 244Gl Diesel