Inserting Rear Window In New Convertable

Hi There,

Just Installed A New Softtop And I'm Really Pleased With It Just A Little Frightened To Cut The Hole To Reinstall The Window, At The Moment It Is Attatched To The Existing Headliner and wooden window frame Which Was In Good Condition.
Anybody Out There Had A Go At This, I Could Do With A Little Advise Beforei Get The Knife Out! I'd Hate To Mess Up A Perfect Roof!

Thanks
Steve