They are not going to be built, you will need to build them. I am sure they will do it for you but there is a charge for it.
AFAIK, you can send them in and they will build them for you. No one is going to sell you complete units.
For an early car you "unscrew" the housing take the old insert out and put the new one in, if you have a big enough set of channel locks it is about a 20 min per side venture.