Perhaps from performance standpoint TTI headers are not the be all end all for an all out effort race car. I think very few would fall into this category of necessity, and therefore TTI are likely a good alternative. In my 69 Swinger, yes 4 speed, yes scattershield I didn't find the install or accessibility to anything to be a problem. Now on my 73 SS/JA Duster, I agree I wouldn't run TTI on it when every little bit counts. It uses Stahl headers with a tube that goes around the frame. I also have Hooker 5303 race headers, I can assure you those are an ugly install even with an automatic. Again, don't think this is what the masses are doing.
