When installin g TEIN coil overs do you have to reuse some parts from the OEM strut assembly? Also, how many inches of drop does the TEIN CS give?

No, you do not have to reuse the tophats for the Tein's, they are a full replacement.

I'm not sure on the exact drop of the CS, but I know a bunch do, and they will chime in soon.

actually, i wanna clear it up. if you get flex or cs, no, it's full replacement

however if you get the HA, you have to reuse the pillow mount, etc...

and for drop

http://www.tein.com/lexus.html