Ithaca makes a slug barrel for the nova price $150 then you could take it to a a gandermountain or carlson or ballistic specialties and have it painted camo for less than $100
I would use a decent saw maybe one of the model train ones they use to cut plastic. start off by cutting maybe 1/4"sand it down and see how it feels and looks.
So basically you want to combine a tactical shotgun, skeet gun and trap gun. Thats basically impossible inless you buy 3 shotguns. Any shotgun will stop a intruder anyways you don't need a short barrel to stop a criminal.
Go with a sporting shotgun
Browning sporting models
Citori
Gold
Cynergy
winchester models
Super x2
select
energy
beretta
391
687
benelli
sport 2
franchi
alicone
612