Normally, the pipes just push into the heads. Even if they have been retained with exhaust cement, they usually come free after being given a good wriggle. Having said that, that clip is not standard, so could be clamping the pipe onto a stub in the head (maybe the pipe is oversize and clamped onto a stub of the original pipe). The diameter of the standard pipe is 1 3/8".
Hope this helps,
Regards,
Eddie.