The stoptech st-40 kit uses their proprietary type of rotor/hat, not c5.

You just have the calipers/brackets?

If I were to do it from scratch i think Delaney's adapters with c6 race hubs is plug and play.

I currently run a diy 3rd gen spindle with non 1le hubs that have been modified to take 1le out bearings. It's a lot of maintenance and weight over the c6 adapter kit IMO.