Questions on body work

I am starting to do some of the body work on my 66 Dart. a Long time in waiting for sure. Been in primmer for 5 years now. I am going to use a itching primmer I got from Napa. Now I am understanding I can do body work over it after it is applied. Is this true. Plus on my hood around the scoop there is bondo. Will that all need to be removed first, or can I just spray right over it and then apply the fiberglass.

Also what is the best thing to do when molding in a abs hood scoop. It is installed from the bottom side as I was having problems with it wanting to crack in the corners when installed just on the top and then fiberglassed to make it look like part of the hood.