Why didn't you contact Serbu with your question?
There is no reason they couldn't use a left handed 870 to make a Super Shorty. If you provide them the gun, they can make it into a Super Shorty registered short barreled shotgun. $200 transfer.
I don't think any pistol grip only lefty 870s were ever made, so no AOW for you...
"9mm has a very long history of being a pointy little bullet moving quickly" --Sevens