I use them on a 68 cuda with 446 Stage VIs, well built, thick flanges.
If you buy them, then you install ,put a good dose of anti seize on your collecters, when you plug in your 4 tubes, Makes it a lot easier when you need to take them apart a year down the road.
Yup, He's right. The ones on my Dart won't come apart, or wouldn't. I'm sure with some heat and a bfh they will come apart.
They also suggest putting them on the engine outside of the car, and tweaking them, before you attempt to put them in the car.
I should have filed the the tubes down in some places, cause they did go together hard.