I'm in the middle of knocking off a Stickley knock-down even arm settle. Since this thing is almost 8', I'd like to add some cross bracing to it rather than just rails along the front and rear for the upholstery frame to sit upon. If this was a glued up piece, I'd use pinned mortise and tenons. However, this is a knock-down piece and I'd like to keep it as easy to transport in the future as possible. Essentially, it'd be nice to have the lower rear and front rails be separate for moving.

Since I've never actually seen an original, and I'm going off of pictures and dimensions, I have no idea how they dealt with this at the start of the 20th century. The ones I've seen are not knock-down and so there's a center divider in place to keep the front and rear from spreading. Thoughts?

Picture so you can see what I'm dealing with.