Forgot to post this up here! I spent some time building up an ideal primary shotgun and I'm pretty pleased with the results.
It was once a PPS 870, but has since had 90% of its guts replaced with real steel (trigger set) and custom machined parts (firing pin and other upper assembly pieces). Externally, I replaced the outer barrel with a much nicer tanaka one, and added an Alpha Parts stock adapter, a clone of the RS Mesa Tactical adapter. The full length rail and mag extension were bought from S&J, a Canadian parts manufacturer known for their cool shotgun shit.