All journals are measured as well as the parts to be pressed to make sure the fit is correct. We set the headspace and check it twice with a GO gauge, with a live round (not fired just for testing the bolt closing) then with a NO-GO gauge. After setting the headspace we drill the barrel pin hole and ream for the new barrel pin. The pin is pressed most of the way through so you can press it back out the same way it was put in to remove the barrel for installing rivets. If you don't want to use rivets then just press the barrel pin the rest of the way in.
The rear sight, gas block and front sight are pressed on after the barrel pin is installed to make sure everything fits correctly on the barrel. We use a special fixture to press on each piece to ensure proper alignment.
When reinstalling the barrel I recommend to use a headspace gauge again to make sure you install it back to the original setting.
The parts kits come with just the main parts, no rivets, no center support, no receiver flat, no rails and no tools.