Although the Shannon 39 and Morris 38 seem superficially the same size, I think the Shannon is a fair amount larger. According to published data, it displaces almost 20% more than the Morris.
Both boats are evolutions of nominally smaller boats by the same builders. The Morris 38 evolved from the 36, but was otherwise very much the same in many ways. The transom was extended, and the deck was revised, but in the same way the 32/34 are virtually identical from the aft cockpit forward, so too are the 36 and 38 near twins.
Shannon started with a "full keel" 38 (I use quotes because the keel isn't "full" in the strict sense of the term), which later evolved into a keel/centerboard 37, and now into the current cruising fin 39. There have been rig
advancements along the way, with the early boats being cutters or ketches, and the latest iteration normally being double headsail sloops or ketches. Down below, I believe the space available for accomodations has been pretty much the same from 38 to 37 to 39.
I'd be surprised if either the Morris 36 or 38 have room for a diesel generator and A/C. Many have been built with A/C, but only for dock powered use. Maybe I'm wrong about this, but I suspect you need to be in the Morris 40/42 (or better yet, the 46) to have room for a generator. Those boats have much more displacement than the 36/38.
While the Shannon 38 is pretty sizeable, I'd also be surprised if you could fit a generator in one of those without giving up lots of space you'd otherwise like to have. I suppose you could sacrifice a quarterberth for generator space, but I don't remember seeing any of that series Shannon with generators. It may well have been done, and I'm just unaware. I do remember seeing some of the 43's advertised with generators.
I think very highly of the Shannons, and considered buying one myself many years ago. They're nice boats. In my view they are probably more of a pure cruising boat than the similar sized Morris boats. According to NE phrf ratings, the Morris 38 is almost 30 seconds per mile faster than the Shannon 38. The finish work on the Morris boats is a little better in my opinion than found on the Shannons.
I'm not sure why there is such a price differential right now. One of the Morris 38s, Alacrity, which is a current listing, is a boat I've been aboard. It's eye-poppingly beautiful, but a lot of money at 390K. I wish I could afford it.
There are two slightly older Shannon 39s presently listed at 215K. Some of the difference may be due to condition, sails, electronics, etc., but there's no denying in the current marketplace the Morris boats are more expensive than Shannons.
In fact, there's a 1997 Shannon 43, which I think are extremely nice and spacious boats, listed for less than Alacrity.
Part of the answer may just be supply and demand. Last year I thought the Morris 46s in the used market were attractively priced. I remember one built in the mid 1990's was asking 425K. That is much more boat than the 38 if size is important. All three of the 46s that were for sale last year are now gone, and the only one left is a recent build and much more expensive.
I suspect the large number of Shannon 38s built from 1978 or so forward tend to depress the value of the 39s. There are usually quite a few 38s for sale at any given time, and the asking prices tend to hover around 100K, plus or minus.
Asking prices on the Morris 36s seem to have been rising pretty steadily for the last 5 or so years. I remember when I bought my 32 in 2000 that a 36 could have been bought for 150-160K. Now the asking prices tend to be quite a bit higher, often well into the mid to upper 200K range. I don't know what the sales are actually closing at, but a broker could tell you that.
Good luck in your search. You have your sights set on two top flight builders.
I keep my boat near Canaveral. It's not a terribly fancy finish inside compared to many of the more recent Morris boats, but if you'd like I'd be glad to show her to you. I also suspect Morris will be at the Miami Show in February with one or two boats. Shannon is usually there also.