Assuming the design is the same as mine (CL3), there are four major pieces you need - the motor, attached to its mounting plate; the pulley housing (headstock); the headstock saddle that sits on the bars; and the clamp.
Be careful not to mix up the clamp with the clamps for fixing the rails.
If you've got all those pieces, and the bits to screw them all together, then what I would do is get the saddle on first, then the headstock *without* the motor, and then get the clamp on and tightened up before you add the motor.
If the motor and headstock are already attached and you don't want to take them to bits, you'll have a much easier time with a partner to help mount the headstock. It can just about be done by one person but it's a heavy job.
Last tip - if you need to dismantle the pulleys, be aware they are held on by two grub screws, one on top of the other.