The Merlin camshafts are all driven by a combination of spur gears and bevel gears. A bevel gear on the main crank drives 2 vertical shafts, one lower one upper. The upper vertical shaft drives another bevel gear which in turn drives 2 angled shafts, one for each of the 2 cylinder head banks.
Both magnetos (one on either side of the engine) are driven from a lateral shaft which is driven from the upper vertical drift shaft by a pair of skew (helical) gears. I believe that both magnetos share their drive from just one set of the skew gears.