Fabricating my Swingvalve to exhaust

[Xtrempickup]

I need to fabricate my swingvalve for my tranny buster. I found the parts i need to do it to my downpipe, but i have questions about size. If i have a 2.5in flange, do i get a 2.5 in diameter pipe to weld it to? just making sure before i buy my pieces and then how do i go about getting the o2 bung welded, drill a hole first or what>?

[Speedeuphoria]

yep should be 2.5"

yes drill a hole(rota broach works well or step bit), they recomend that its not on the bottom of the pipe, so moisture dosent collect and prematurely end the o2 sensors life