I've done a "cut and shut" on one of my Duke of Edinburgh WWI AC hulls, lengthening it 1" to make a Defence Class AC hull. Ralph Coles cut a few hulls in half to ship to Australia and we used the same method, though I'm not sure what Dreadnoughts Hulls does.
We glassed brass tubes lengthwise inside the hull across the point where it would be cut in two: 2 at deck level, 1 at the keel and 2 more where the hull sides met the bottom. The hull and tubes were carefully cut in half. To reassemble, the next smallest tube size was inserted into the bissected tubes, restoring the hull allignment and the areas between the tubes were fiberglassed. Next the tubes were removed using a dremel and those areas were glassed, then a final layer of glass was laid all along the joint. (If desired the brass tubes can be left in place for extra strength.)
Bob P.