Actually the rear cross member was plan B. We were going to use the stock cross member and do a few minor mods. When we were cleaning out the garage the stock one got put in the scrap pile by mistake so making our own was our only choice. We determined the height by setting the spring and figuring out about how much it would compress under load and you're right that it is about the same height as the stock one.
It's kinda funny because my wife gets upset with me because I NEVER throw out anything and wouldn't you know, the one thing we needed got tossed out!