Questions about 3" downpipe

[PSU 98]

Anything I should know about before ordering, or are they basically "bolt and go" parts?
I see some places offer to have O2 bungs welded in, different puck sizes, etc... Don't want to order one and then find out I made a mistake.

 

[ZNix]

Get one with a bung welded in for a WB02 sensor.. Buy a M18x1.5 oil drain plug, and put it in there. Its much easier to buy it that way rather than have someone else weld in one when you need it.