It has a backbone main tube that is ovalized at the back to mate with a small upright "seat tube". There will be two small rectangular towers with a connecting tube between them for mounting the seat, and since the towers sit on the tapering ovalized section of the main tube even their ¾ inch thickness was enough to require two different miters on the two sides of a single tower to fit right! Mark said it didn't take too long because he used a bench grinder with a narrow, rounded wheel (ie. no repeated clamping and unclamping in a vise) to make lots of small cuts with trial fittings between.

The rear upright is open on the bottom so they will be able to make a special workstand fixture that just plugs into it, since commonly available (ie. cheap) workstand clamps wouldn't fit such a large and oddly shaped tube.