The cam is the first part to be fitted. If the timing gear has been removed then it is important to check that the oil pump drive groove on the camshaft end points towards the mark on the gear. If there is any wear to the groove then the cam should be replaced to avoid problems in the future. The groove is where the oil pump drive fits and wear can lead to the loss of drive to the oil pump and certain disaster.
There are 3 possible ways the timing gear can be put on and only one is correct. If this is not lined up correctly your engine WILL NOT run. Use new lock washers for the 3 cam bolts that attach the timing gear. Torque to 18ft lbs. The bolts should be 14mm across flats.
Cam and timing gear in place.