I bought a new 66 master cylinder for my brakes and new brake lines, but the brake line does not fit the master cylinder. Both the brake lines and master cylinder are the correct ones. I traded my old master cylinder in when i bought the new one so My question is was there a fitting or something that I am missing on the new one?

 

The 66 had a larger steel line running from the MC to the divider block than did the 64-65. You may have been sold a wrong part, or there may indeed have been a brass fitting on the old MC you need.

BTW, you violated rule #1 of auto repair- Never discard ANY part until the car is going down the road.

 

You should return it and switch over to a dual bowl MC for the added safety it provides.

 

+1 on the upgrade. Pick up a 67 M/C and do minor plumbing to make it work. The only challenge is you need your 66 pushrod to make it work.