"ribs don't appear to be tapered"
Yes, that was one of the reasons to ID as Charles River-area. The others - (1) gunwales are chamfered on inside bottom edge except at thwarts (and presumably seats... cannot see in photos), (2) thwarts look like from some CR builders, (3) seat caning style and pattern, and (4) presence of canopy mounting brackets attached to gunwales. These brackets were readily available aftermarket to anyone, but are most commonly seen on CR-area canoes.
H