I am currently having a go at fitting the zspeed under tray on my 350. The old plastic one was flapping in the wind.
After removing it, (had it up on axle stands), not ideal but doable for a guy my age and size. Old and Fat.
Found that the 2 bolts, below the radiator had sheered off, grr. got to borrow an angle drill now to drill them out.
The fixings on the wheel arch liners area bit iffy too, going to beef them up with a little bit of plate slipped between the nut and plastic.
So taking my time and fitting it securely. Just wish that the last person had done the same. It was regularly serviced, but just goes to show that not everyone looks after your cars.
Go to say though the zspeed under tray looks great.