It is easier to set the alignment marks prior to the removal of the cylinder head and cam removals. Keep in mind that when the camshaft alignment marks match the "V" marks on the top cover of the belt, the engine is not at TDC. It's actually slightly off of TDC.

You can certainly reset the marks afterward, however, make sure you properly align the crankshaft mark, and then align the cam marks and place the belt over the crankshaft working in a counter clockwise direction. It's difficult with the S70/V70 and 850s as there is only about 1" to maneuver. After you have the belt in-place, release the tensioning unit and spin the assembly 1 to 2 times. This way you'll be able to re-check all alignment marks and also tension the belt.

As you turn the crankshaft CCW you'll be able to feel the compression if spark plugs are in-place. I believe you'll need a 30mm sprocket and a medium breaker bar.

Good luck!