I've seen someone on ebay selling a new and improved Z bar kit for the 67-69 americans. I have the link saved somewhere. Pretty neat kit that should hold up to the strongest of pressure plates. It's not cheap but if you are building a car it might be worth investigating. Used ones are hard to find and they were flimsy built any way.
By "Z bar" do you mean the clutch linkage bellcrank that pivots between the block/bellhousing, and the chassis?
No wonder I could never find one, that's two people calling them "Z bars". A Z-bar to me is a bracket bent into a .... Z shape. A bellcrank is something that pivots and has usually two radial arms.