Antenna men for mobile?

I do it often. Depends on the vehicle. No such thing as a "universal" antenna.
Whenever I build something for a commercial tractor it's always custom built to the vehicle itself for that vehicle only.

 

What kind of vehicle?

 

99% of the shops and “techs” lack sufficient knowledge about antenna systems and feedline, most are still learning how to spell analyzer.

 

I have a quick and easy suggestion for you. The easiest solution for that truck would probably be a 102" whip with a 90-degree Bend at 13:6 to stay under your height restriction.
You could probably fabricate a mounting solution similar to this one. It's just a flat piece of stainless steel bolted to the factory mirror arm and extends out from the arm a little bit far enough to where you could bolt a stud on to the mounting plate since the factory mounting location doesn't give you enough clearance to put a stud on similar to this one, and the factory stud wouldn't be strong enough to support the weight of an antenna long enough to be the physical Dimension it needs to be to reach your height restriction.

81 inch stainless steel and copper t-660 antenna by Jerry by rabbiporkchop posted Feb 13, 2012 at 2:56 AM

 

Bending the whip shouldn't cause any issues and I know a guy with a Freightliner Cascadia and I heard him 74 miles down the road on his Barefoot Stryker 955 with his 9ft whip flopping around in the wind at 70 miles an hour so it was working just fine.
This guy has the same truck as you and you could check out how he did his bracket. I would do it differently. I would unscrew the four bolts that hold that mounting plate on and then I would take that metal piece off and use it as a template and trace the outline onto a piece of stainless steel.
Doing it my way would prevent you from having to drill through the mirror bracket the way this guy did.