[fanaudical]

In addition to speaker selection (I put some Boston Acoustics in my '75 - reasonable price, sound OK) also look at mounting. There was a thread here related to making some plates to attach to the door frame for mounting the speakers to improve sound quality and reduce install headaches.

Some relevant older threads:

http://forums.pelicanparts.com/porsche-911-technical-forum/778272-door-speaker-spacers.html

http://forums.pelicanparts.com/porsche-911-technical-forum/968690-its-time-get-some-proper-tunes-car.html

http://forums.pelicanparts.com/porsche-911-technical-forum/941691-door-speakers-1974-911-a.html

http://forums.pelicanparts.com/porsche-911-technical-forum/955703-front-door-speakers-recomended.html

http://forums.pelicanparts.com/porsche-911-technical-forum/844347-door-speakers-what-fits.html