It is not possible to have lower anchors retrofitted, only tether anchors can be retrofitted.
You might want to browse this thread
Radian Successful Install Thread - Car Seat.Org - Carseat, Vehicle & Child Passenger Safety Forums to see if anyone has successfully installed a
Radian in a QX4. Not sure if it's in there, but it might be worth a look if it is

. And you could check to see if your friends' vans are on there too.
Just so you know - the
Radian 80 is the same seat as the
Radian 65, just with a higher weight limit. Most kids outgrow carseats by height before weight (certainly your
DD will from what you've described!). So she'd probably outgrow the 65 by height before she even reached 65 pounds. I know there is a significant price diff between the 2, so wanted you to know if you want to save a few bucks. Unless you just gotta have that adorable Princess cover that is only offered on the 80!
One of the big differences between the
Radian &
Britax seats is that the
Radian does not sit up on a "Base" like the
Britax seats do. Just a personal preference thing one way or the other, just a diff between the 2.