<VV> Windshield pillar weatherstrip adjustment

[Les]

When installing the weatherstrip up the rear side of the windshield 
pillar ('65 vert) the chrome weatherstrip retainer installs first, then 
is fastened down with screws, then the weatherstrip glues into the retainer.

There is quite a bit of adjustment available to move the retainer 
around. How do you know where to put it, when you can't get to the 
screws to adjust it once the weatherstrip is in place?

Thanks,
Les
1965 Canadian Corsa vert 140/4