Don't ever give up on something without testing.
If you have the dash pad off, place the speakers in the dash location where the tweeters would go, and place around with a couple different mounting points, and listening to the speakers in those positions. As for the tweeters in the a pillar, you can use some temporary mounting adhesive to place the tweeters in the desired location, and aim them the way you are wanting to place them, and see how they sound with the speakers in the dash. This is just my point of view on things...