Thought about going to a PGO Mossberg 500, but then questioned its true utlity.

Miraculously, this dumb idea popped into my small brain:

16.1" barrel (this will be cut down from a 20" donor) and ATI collapsible folder stock.

This would allow me to shoulder the shotgun when deemed necessary and still have the shortness of the PGO.

The only question would be the legality of the setup when the stock is folder, as the length of the shotgun will be under 26".

Your thoughts?

18.1", as 18" is the minimum length for a shotgun.  16" is minimum for rifles.

As to OAL...  ATF regulations on this have always stated that the measurement of the firearm be taken in the "firing" configuration, meaning stock unfolded.  NJ makes no such distinction.  It's yet another one of those questionable areas.  I'd say if the gun is capable of being fired when it's in a configuration that's less than 26" OAL, a prosecutor could make an issue out of it.