Over on page 2 of my SS Ohio build log in Working Vessels, there are a series of photos of the join that self aligns, then bolts together On Ohio much filler was still needed to make the joints good. this is because she is a timber build.
We have fitted a joining bulkhead to at least two models, which were already built and sailing. this required a precision bulkhead to be built, with a self locating key way face. Then a second, opposing bulkhead to be laminated off of the first one. These were built slightly over size, and separate from the model.
A cut line was then marked around the hull, accuracy being important here. The next stage was to drill 0.5mm holes around this cut line, into which 0.5mm piano wire was routed across the hull. This is used to face up the two bulkheads to. the 0.5mm wires. (It is worth drilling bolt holes through the two bulkheads as they are together, before fitting the bulkheads into the model.) The bulkheads are then fitted into the model, either side of the wire, and bonded in to the hull. Much care needed here to ensure a very good bond as well as accurate fitting.
The piano wire is removed from the model. this should leave you a 0.5mm gap between the bulkheads, which is your cut line. Once the hull is cut, some fine finishing will still be needed with filler etc, to get everything looking just right.
With this method, it is worth cutting where the sides are near parallel, with little or no tapering towards the bow or stern, as removing 0.5mm from a tapered end will cause a step to appear.
Alternatively, the joint could be disguised by some type of down pipe or garbage chute, lifeboat runner or camouflage colour change on a warship.
I shall try and find some examples to photograph, within the group.