I have been running the spitfires in a 63 dart for almost 2 yrs and I am very happy with them. It does take a little work to set them up right but, For a mild to mid level performance engine they are a good buy. The only issues I had was the tight fit on the passengers side manifold area that required the exhaust manifold studs to be removed. I am using allen head bolts to adress some of the tight areas around some of the tubes on the mounting flanges.Also You have to modify the steering coupler to clear the headers. Abodyjoe has an EXCELLENT thread on the installation. I have not had any leaks or loosening since the install. I know there are other options out there but to say that TTI is the only choice is not correct........