'77 Spider - Top Header Seal Replacement

Am about to undertake replacement of the rubber seal between top header and windscreen top frame (fitted to leading edge of top). Need to stop the dribble which occurs in rainy weather, and ends up in my wife's lap !!
I have a new seal on hand, but have not started removal of old seal - I have undertaken this process before on an MG (heresy, I know), but never on an Alfa - is there any sage advice out there, any pitfalls to avoid ?
One concern is the thickness of the new, 'puffier' seal compared to the old - the top now requires firm effort to latch closed; I can't imagine what it will be like with the new seal installed !!
Anyhow, any advice appreciated before I tackle this job at the weekend. Cheers...

It should be a pretty easy job, the most difficult thing is to get rid of all traces of the old glue. Remove the the existing rubber carefully so it doesn't disintegrate and pulls off as much of the old glue off as you can. It should be stuck to the hood material that has been folded over the metal front of the hood frame - try not to disturb this as you clean off the old glue.

When re-gluing use something like Evo-stick contact glue and put one coat one each surface, let it try and then put another coat on and also let that dry before sticking them together. If you don't get it right you can pull it apart and try again but you will have to clean off the glue first.

I refitted my old front rubber when I did my top so I can't say if it is best to trim it to size before or after you glue it on.

Thanks Cosmo for the tips - sorry for my late response. I will make an attempt at it this weekend. Have the correct contact adhesive from a previous weatherstipping project, so that should work OK. I wasn't sure if there was a metal channel required as well as the rubber part, as I saw this listed in the Classic Alfa parts section.
Cheers...

Finally got 'round to doing this job; there is a metal channel, riveted to the top header, into which the seal will slide. Old seal was just glued on top of this channel ! I used Autoglym Bumper Care (all I had lying around) to lube the new seal, and help it slide into place into the metal channel. It was a bit of a tug-o-war, but I won in the end. After trimming, looks great - and is water and air-tight now. Highly recommended, if your header seal is looking a bit petrified...makes the car so much more comfortable.
Just make sure you get the seal right way around, with lip towards the front, before sliding into place.