If you're looking to position the engine for belt replacement, unscrew the centre inspection screws (the one
between the mounting screws (21) from the camshaft end caps (20).
Line up the crankshaft mark. Get two 6mm drill bits and insert a shank into each cam cap. If the front cylinder is in the correct position then the drills will engage into holes in the cam ends and lock them in place. If you're unsure, remove the drills, rotate the crankshaft 360° and try again. You can also use a torch and look through the screw holes. You should be able to see the cam holes when they're in the right position.
The camshaft holes will only align with both the end cap holes when the crankshaft is in the correct position.
If you need to then position the vertical cylinder at tdc on the power stroke, then just rotate the crankshaft a further 270° from the horizontal cylinder tdc power position.