It looks like a Stevens butt plate. Stevens bought out the assets of Mass Arms in the mid-1890's. Is it a factory job after Stevens bought them or a Stevens factory replacement or was it made that way by Mass Arms with a butt plate acquired from Stevens? I don't know. Mass Arms most likely did not make butt plates, they probably bought them and they would make almost anything a customer wanted within reason. Unfortunately we can't get a factory letter like on some other manufacturers so we'll never know.

I agree George. The gun has the full round barrel like a long range but then only a 40-40. And nothing else makes sense. Strange.
I am wondering if it isn't a put together gun by Stevens from parts as Deadeye suggested.

Wondering if the terminology is the only problem here? Whether it's a "longrange" or a custom build, it still appears to be original, and I'd assume from the age it's factory done? Does that really make it wrong, or just wrong to be called a "longrange" model?
In most cases the old factories didn't waste anything, and also had no issue with building to a customer's request. This could be a case of assembling factory parts to a customer order. Or it could be a case of using parts on hand to assemble a gun. Either way, I wouldn't call it wrong, just not what is usually expected to see in a certain model.

Marlinguy, I agree that the rifle has been in its current configuration for a very long time and possible since it left the factory. And it could be a special order as suggested. 

My only question was in regards to the buttplate. As I said I had never seen one like that before on a Maynard. The interesting info to me was the Stevens comments which make sense to me.

I was at the gunshow in Hutchinson Mn this morning and this gun was at the show.
It is definitely factory or at least been like it is for a very long time. The buttplate is by all means Stevens (at the show were 2 ea #44 Stevens and they all had the same plate), it was nickel plated and has worn a bit. The bore is quite shoot able but not mint. Nice old gun, very heavy barrel.
Thought you would want to know.