I took out the three large round bar concaves that are used to thresh corn and beans and then started to put in the three small wire concaves that are used for oats and other small grains.
The manual makes this seem simple. Maybe simple, just not so easy. Especially to get the concave cinched tight to the back of its nominal position. But its in, the other two should be a bit easier to do.
Dad/Gramps helped put it in and came by at the end of the above video to say hello.
Here's a short animated video of how the concaves, which are set just below the front of the spinning rotor, work inside a slightly new version of my combine. The mechanisms are very similar.