When applying under express entry, there is no primary NOC. You will just need to list all your skilled work experience in NOC O, A, and B to get the total work experience. It will be a lot clearer to you once you actually open a profile in the system.
They still use the 67 point scale to assess eligibility under FSW. If you can't score 67 points, then you cannot enter into the express entry pool under FSW (you might still qualify for CEC if you are working in Canada). Once you are found eligible under FSW (that is more than 67 points), then you are awarded a score out of 1200, which is used to compare you with all the other applicants in the pool and to send invitations to apply.