Well, tough call on many levels.
The first red flag I see in your post (well, not a "red flag" but an area of concern, anyway...) is how you come up with $1,100 because if you are over-valuing the stuff you want to trade him, maybe he's over-valuing his gun.
You have to be fairly active in the market to have a real handle on what is truly WORTH $1,100, is all I'm saying.
Next, though he has no box, we have no idea truly what condition that Model 27 is in. Tossing out the term "MINT" doesn't tell the tale. Unfired? Seems odd that it wouldn't have the box. Turn line on the cylinder? Chips in the left stock from ejected rounds? Evidence on firing on the recoil shield? Any/all of those means that it is not "mint."
Anyhow, it's kind of a tough question to answer given what we have to work with.
But it does often appear that most revolvers in 8-3/8" barrel length tend to be worth a bit less than a traditional length, generally speaking.