Not a good idea. he Montana does not have near the frame to support that much load on the rear end even with "beefed-up" suspension. Next issue is that much weigh on the rear will unload the pin (think see-saw) and cause ride and handling problems.
I look at this as a mechanical engineer. I would never swing that much weigh around on the back end.
If you want to go the route of a 5er, you need to look at New Horizon and have one special built with the lift that has the frame to handle it.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot