You can see there's a bar for doing chins; the position is a bit different than it looked on the power rack plans. The easiest solution ended up being to fasten the bar to the top of the posts.
The bar is the same as the safety bars, a 36" length of steel plumbers' pipe. It has a 7/8" interior diameter and a 1 1/8" exterior. It's strong enough to support my 240-pound neighbor doing chins.
We fastened the bar to the top of the posts by drilling a hole through each end and then nailing it in place.
We put a wood screw into each post on the side for an easy place to hang the bar clips. There's also another hook on the front for hanging stuff on as well.
At the front, the two posts started to move inward at the bottom a few inches. We resolved this by placing a loose board between them. It's a 1" x 6", and, as I mentioned, just sits there. A more elegant solution would be to get a 1" x 4" and actually fasten it in place.