Back in 69, I was 18 and bought a new 69 Barracuda Formula S 340 4 speed. Nobody was making decent wheels for 5x4, so I got a set of American Racing Torque Thrusts with adapters. It looked amazing. Back then I knew nothing about adapters. I kind of doubt that they had billet adapters back then. My RF wheel almost fell off. Luckily, I was on a city street. It was wobbling really bad. It turned out to be a cast metal adapter; don't know the metal type. Nobody told me to retorque them. I will agree with you that a billet adapter would probably be perfectly safe.