Since we last had the discussion about 8020 and rigidity, and about using struts to brace the gantry, I bolted my unit together. I am very pleased with the 8020, and I only used 1530 (1.5" x 3") instead of the much stouter 3060 that you have.
I don't understand what you mean about the z axis. I took the common? aproach and made a plate that slides up and down, with the headstock or router/whatever attached to that. How do you plan to do your z axis? Do you mean the whole thing would move, including the z axis motor?
I have some pics of my current build here if you want to see how I did my z axis using a slide:
http://www.cnczone.com/forums/showthread.php?t=57673