-----Sam,,,The headers do bolt on, but you also have to cut the front pipe and do a bit of welding. That might be something to keep in the back of ones mind. For instance, if I had just spent the bucks install a Gardener setup I sure wouldnt be hacking on it. On the other hand if the front pipe is already compromised the decision would be a bit easier.
-----I had headers on my 64 421HO GP for the first several years and never liked them because the pipes hung down low enough that I had to be careful going over certain bumps or risk flattening a tube or three
.........Bill S