You use the entire thing..
What I did:
Cut the tstat with cut off wheel, cutting off the part I wasn't using in my setup (the heater hose connections):
Then let it sit on a sanding wheel to machine the surfaces level, welded it in my desired angle:
The holes on the flanges don't line up, you have to VERY lightly ream the holes towards the center, doing a little bit at a time until it works. Bolt it down with 3800 gasket (+ sealant) and use socket cap bolts.
[This message has been edited by sco77 (edited 10-01-2013).]