2006 Legacy 2.5i EL to UEL

[AR2.5i]

Alright so I've been reading a lot on this section about UEL's on 2.5i's (Thanks GEE-OTTO and others who contributed).

 

I have already ordered the following parts:

• Stock WRX manifold
  
• (2) O2 bungs
  
• 36" O2 Sensor Extension
  
• 1/2" thick 3 bolt flange
  
• 2.25" 3 bolt gasket
  

 

I will be taking this to a shop and I understand that the end of the manifold will be cut off and have a flange welded in. If I'm understanding correctly, doing this will remove my first cat? Also the 2 O2 bungs will be welded in different locations. One on the welded piece between header and midpipe, the other before after the second cat? I feel dumbfounded but I also think I kind of understand it so far. Thanks for any help.