I've run tons of AV-Gas.
The "LL" stands for low lead... but, it's still 4-5 grams per gallon, which is quite high by automotive standards.
Av-Gas is a more precise fuel than auto gas. It is also blended so it doesn't vaporize quite as easily as pump fuel... (you don't want a vapor-lock at 10,000ft!) All this really means, is if you are running straight Av-Gas, cold weather starting might be a little more difficult. Personally, I don't keep snow tires for the mustang, so it doesn't matter.
But, any problems of this sort associated with running straight av-gas disappear when it is blended with automotive pump fuel.
My tow vehicle likes to ping with a load, so whenever I take the mustang anywhere, I dump in 5 gallons of av-gas with each fill up. It cures all problems.
I've also run it in the mustang quite a bit. It's heads don't have hardened seats, so I figured the lead would do them some good. It has no problem with Av-gas... even straight.
I've got eight 5-gallon gas cans, and take them to the airport in the back of my Pontiac Parisienne. They allow me to back up to the pump and fill them all. They like moving as much fuel as possible. It keeps their stock fresh.
It also works great in those old shovelhead Harleys.
It's by FAR the best, along with being a very cost effective octane booster. I highly recommend it. They guy at the airport said they sell quite a bit of fuel to musclecar and dirt track guys.
2-5 gallons with each fillup should do ya'.
Good Luck!