I have JBL 16.5 components in the front with adapters that i got from ebay quite easy to fit just screw the bracket in the existing holes then the speaker to the bracket, then fitted the tweeters where the old ones were.
I also have JBL rear speakers they are 6"x4" got them from ebay quite cheap, combined with front speaker they sound loads better than the origiansl which are just poo.