lots. As with any other later A header, the tubes will either hit the frame rails, torsion bars, center link, pitman or idler arms, and mostly the steering gear. As you know the steering box is almost below the 3/5 ports on the 66, the 69 has room for tubes to go down between the gear and the block. SO...Save yourself loads of grief. Sell the TTI's and purchase Dougs, Some used spitfires, or run large Dakota logs. Fenderwells, Hooker 5208. I modded some later Hooker Super comps and ran into trouble at: steering box, idler arm, pitman arm, and centerlink, so just about everywhere, but the passenger side fit right in if you dont want to steer. Youll see exactly whats need to be lengthened once you get the pass side in, not hard, but it takes alot of measuring, grafting and welding.