The engine is the same they are both "S4QL Mitsubisi" so I suspect that all the parts that bolt to the engine are the same. I would also suspect that the drive train is the same also. The only parts that would be different is the attachments(front loader,ext.)and body parts. Some body parts are most likely interchangeable like fenders and so on. To keep it pretty you would have to paint those parts.
In another thread,I told about my experience with the replacement of my engine on my U4984 Montana. All the parts,new short block,seals and gaskets came from LS.
Reading the spec sheets they do look different,Montana even claims more HP.The lift is different as with the length,and other specs. Most of this is probably due to how the 2 make their claims.
The best way to find out is to contact an LS dealer and ask them.It may be best to find one that carried Montana. Ma-be even an E-mail to LS.