At one point I did weigh the rear of the car and the front of the car to get proper spring rates for the car because nothing is made correctly for the AWD. You might find this info in one of my threads on MO about my k-sport screwup.
As you have pointed out you will need custom spring rates. Honestly going beyond stock info I couldn't help you in this department.
Even with adjustable damping it won't be enough to cover the weight difference between the awd and 2wd.
You are correct the strut itself is almost identical. The real difference between the two is the spring rate. At the time I delt with this the k-sport didn't offer a matrix coilover. We used the one for the corolla for the 2wd guys. I decided to try the celica coilover because, 1. I didn't have 1200bucks for tein coilovers, 2. I didn't have 1200 bucks for teins
(they are now in the 800bucks range)
So I got the celica coilovers which if I recall correctly had 9k front and 7k rear.
If you look at the corolla spring rates the rear was 6k, which is fine for the 2wd but isn't strong enough for the awd.
I had no issue with the front coilovers. The rear 7k that came on the celica coilover. That spring rate wasn't strong enough. I needed 9k for the rear but at the time k-sport wasn't accomidating to get custom spring rates. I kept bottoming out on every bump.
The rear celica coilovers bolted right up no issue at all.
As I said the front bolt holes needed to be larger for them to bolt up. Again this was before k-sport offered a coilover for the matrix.
They now make a set that bolts up with no modification.
2010 Vibe & member of the yeargarage Email me if you need to talk to me, click my siggy and send the email threw the contact page.