When reading that thread I linked in the first post, it sounds to me like the skin if difficult to fit over the gutters and that's why they cut through the centre of the trim holes and then butt welded the joint.
Originally posted buy UPK:
"Followed up on docs suggestion tonight, welded the frame back together, crude i know but needed to study the fit option.
Well after doing that i have come to the conclusion that i dont think sliding on the roof skin can work.
Infact i studied it for ages and i still can't work out how opel put it on in the first place.
Anyhow the long and short of it is that i will remove the original roof as i planned to, cut from the centre of the roof outwards to expose the inner frame weld points, if i am still convinced it won't slide on then i will cut the roof rail edges as per Kev Abbotts method and make a butt joint from front to back.
Don't panick folks if this makes no sense. I will photograph the operation so all will be clear.
One day I will work out how opel fit the roof skin in the factory
and doc, keep using that Jedi Mindtrick, its been useful bouncing ideas around with you, i really do appreciate that. As you say makes me think twice so i only cut once and get it right!!
kev (aka upk)"
Anyway, I still havnt fully removed my original skin (just the tops of the pillars and gutter part to remove). I'm going to start cutting the donor roof later, maybe things will become clearer to me...