I don't think so, you are not altering emissions equipment, only changing the sound of the exhaust by removing a muffler. If you remove the cats, yes. This setup does not have anything to do with the cats.
The current setup doesnt really matter, any exhaust shop will customize the length of the piping when they install the tips. However, this current setup will cost you less to weld on a 325i because most of the work is pretty much done, you can get these installed on your 325i for probably around $30-40. This includes the exhaust hangers pictured for factory mounting point install.
A 323i only has 1 exhaust pipe at the muffler. the shop would just use a Y tube to go from 1 pipe to 2 pipes to utilize the tips. It's very Simple for them to do. There's a local sale pending. I will let you know later this evening.
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