You don't need to remove the clamshell, but it would probably make things easier. If you haven't seen Maurice's guides, here is a link, the pdf's are at the bottom of the page. Now if I could only find an 03/04 top in Graphite Grey!
https://sites.google.com/site/mikefocke2/installinga%2703-%2704glasstopandframeona%2797