HI Todd,
Agreed, your canoe certainly could be an early Old Town, and as you suspect it appears to have had some work done to it. The "slant" at the top of each rib is where the rib ends were thinned and tapered to a fine edge for closed gunwale construction. Another way this was done was to let rib ends into the gunwale by cutting a series of rabbets into the gunwale. Closed gunwale Morris canoes are the most commonly seen like this. Old Town and other builders more commonly did what you see in yours when building in the closed gunwale style.
See here for a discussion of Morris rib "pockets":
http://forums.wcha.org/index.php?threads/morris-rib-pocket-question.16476/
and here for Rushton:
http://forums.wcha.org/index.php?threads/rushton-rib-pockets.18017/
The other closed gunwale canoe in your post #2 above looks like a very original Old Town. Its visible features are what I would expect to see in this canoe if it had not be previously altered. Many features of #1852 appear like Old Town. The thwart behind the bow seat could be original but the stern thwart looks like a later replacement. Early Old Town thwarts looks significantly different from later ones. I don't really know how to describe the difference - older ones are simpler, thinner, and with gentler tapers, somehow more elegant to my eye. If you see them side by side the difference is obvious. Compare the two thwarts on your canoe, and compare the stern thwart here to the ones in your other closed gunwale OT.
The width of the stems suggests outside stems were once there. If the outer face were about 1/4" or so without canvas and 3/8" with canvas, that would indicate no outside stem, but a 3/4" or more outer face suggests an outside stem was there. When you get the canvas off, screw holes will be obviously larger than the holes from the tacks that secured the canvas, and they are larger than ones made for stem band screws.
Those "caps" alongside the decks surely are not original. I've never seen anything like this before and it sure doesn't look up to the standards of early Old Town. The top caps on the outsides of the sponsons are suspect. In my experience, there was a cap only on the outside. I would be these are a later addition. Also, it also looks like there's been some work on the bow stem.
Despite what look like a fair number of changes and some rot/damage, your canoe looks to be in good condition for its age, and you should be able to correct the problems and make it really nice with some time and attention to details.
Hope this helps,
Michael