A lovely cottage in Dana Point, CA, with Gate Arbor #10 shown with the often-accompanying Gate #25.
* The arbor clearance should be between 80-84".  From the top of your posts, the radius height is 1/2" the distance between the posts.  If the posts are 48" apart, The arbor will have a radius of 24".  To achieve 84" clearance, the posts will be cut at 60" off the grade.

CPW Arbors arrive with the mounting caps fixed to the arbor trusses.  Depending on the application, the caps mount to your posts, columns, or wall-tops with either wood screws through the pre-bored holes in the caps, or with the threaded rod shown on the left.  A corresponding hole is bored into the tops of the site posts, allowing the threaded rod to 'seat' itself.  Construction caulk adhesive or epoxy is recommended.  

An example of how the laminations can result in a book-matched affect.
*  5-1/2" width x 2-1/4" thick, mounting to surfaced 6x6 posts at 5-1/2" sq.

Here we see the Garden Gate Arbor #10 with a seamless joint to the site posts.  Without the mounting caps, the arbor truss must be exactly the same size as the site posts.  Our normal thickness of 2-1/4" becomes 5-1/2", and the width also at 5-1/2", to accommodate a surfaced 6x6 post.  All of it amounting to a custom request that will have the arbor truss shipped with threaded rod embedded into the ends of the truss.  A corresponding hole is bored into the top of the site posts and the Arbor is set into place by fitting the threaded rod into the post bores with a little epoxy or construction adhesive.  The bottom edges of the arbor are given a 1/8" radius.  The top edges of the posts should also have this radius, allowing for slight differences in expansion between the arbor and the posts.  

Below shown with Gate style #8, which is Base Cost + 25%