I also found it easier to fit the rubber first, then drop the new pump in... it is fiddly...
There is also a mod you can do with the fuel reading arm, by changing the two over, as the ttrs one i found give a false reading..
Not to sure how this is done, but i'm sure someone will give a better instruction...
Also make sure you have plently of material to catch/soak up the fuel that squirts out...maybe have a bag ready to drop the old pump striaght in to, as the old pump you pull out will be filled with petrol, less mess, open your fuel cap to help release the pressure.
Just take your time !
VCDS is required to adjust the new pump !