I have a Nordic +3 on my 21", and I run the carlson extended choke tubes. I don't have a picture, but it is flush.
I have 8+1 in mine, and am running the stock magazine spring. Has performed flawlessly. I have somewhere between 1500 and 2000 rounds through it. It is more reliable than my friend's 870 pump. I haven't had a malfunction in at least the last 600 rounds. Running the lightest federal loads I can find.
Enjoy!