The cant hovers above the barrel so I don't think it would be possible to put the pin thru it. You can remove a pinned barrel and put it back and not loose POI. If its a dedicated slug gun with a pinned barrel that will never be used for anything else, you are better off having the receiver drilled and tapped.
deernhog and Geybeard are correct in that you should try the barrel out before pinning it. Every gun is different even when they are the same make and model. Pinning the barrel removes the slop between the barrel and the receiver. The barrels are mass manufactured as are the shotguns. You may get lucky and get a fairly tight fit. Some people shim the barrels. Basically, they take a shim of some type and tap it in between the barrel and the reciever. Some people take tape and wrap it around the barrel before inserting it into the receiver. I have heard that both of these methods are effective. It could be one way to test to determine whether pinning the barrel will help. I had my 870 pinned with a hex head machine screw because I will rarely if ever remove it. I absolutely love the results. The first time I shot hastings slugs thru it, I had to change targets after 3 shoots because I could no longer tell were the slug was hitting. It just kept going thru the same big hole made by the other slugs.