I just put my 6.5's right on and screwed them down to the stock plastic 5.25" mounting bezel. You want to move the as far the the bottom and front of the car as possible. Mine is close but doesnt touch the door panel. I plan on redoing it however and cutting half an inch off around the plastic and make a wood mounting plate and glue to the plastic. This way it would still be angled and not be as close to the door panel.
I do wonder about the tweeters however. What do you guys normally do? I like that the factory spots are high but the drivers side points directly into the dash... Right now I have them mounted in the grills in the door. But I'd like to get them higher up