It's not uncommon for Kimber Montanas to be posted as exactly that: A Kimber Montana. As a buyer, since I'm aware that there are two variations (8400 and 84L), I've asked sellers in the past to clarify what model they were selling --- it's part of my due diligence. Since the seller took this rifle on a trade, I can understand that he may not have been aware of the significance of providing details beyond "Montana", and I wouldn't be quick to think that his lack of disclosure re: the comparison to the price of an 84L indicates an intent to deceive --- again, I'd tend to side with lack of awareness.
To the OP, I understand your disappointment, and while it would have been a nice gesture for the seller to refund your money (less postage), I wouldn't hold it against him if he decided not to. Were I in your shoes, I'd feel that the onus was on my shoulders and take it as a learning experience. I think this is more a case of you burning yourself by not being specific with your questions. Bringing up the issues around the EMT seems like grasping at straws to strengthen your argument.
That's my 2c.