Best location is on the mirror brackets as far out as they will mount and not be a hazard. Mount them strait up pointing them slightly forward might gain a little but will increase the chances of breakage. Better bet is taller ideally but probably not realistically tall enough to clear the box by six to eight inches. Usually 48 inch glass whips are the best you will get and keep the wallet happy.
If reception is an issue try running a grounding wire from the antenna bracket to the cabs sheets metal. I had to do this with another truck. Also have the antennas and SWR balanced.
Be careful when it comes to mods like a swing or skip kits they might cause you to run over the legal wastage and you can have problems with the FCC. Peak and tune is usually not a bad idea if done by a good cb shop. Rule of thumb I go by is if the shop doesn't show and tell and disappears in the back room question if they actually do anything. At least have them prove before and after.
Good luck
Bob Wolf
I have always just used a barefoot 29. No mods. I barely use it, but when you need it, it is nice to have.
I had a wilson 5000 antenna, pointed slightly forward on my mirror bracket. Once you were rolling, the wind stood it straight. Every Firestick that I ever had didn't last very long. Broke a lot of them on tree limbs. The Wilson lasted the longest since it would flex more.
The only reason I was looking for a new location for mounting the antenna, was to keep tree limbs from breaking antenna off, again.