After weeks of trial and error, lots of pondering how to do this, and rubbish wet and freezing weather, I've finally got one of the gunwhales fitted.
I wanted to shape the gunwhales into virtually a triangular section and having struggled to bend the full section to fit the hull I decided to cut the approx section first. Had to buy a new table saw tool first though ! (Sarah's away, so I'll need to ask for forgiveness when she returns : ) )
Unfortunately the saw I chose didn't have a tilting table so I ended up spending ages measuring, cutting and rigging up angled fences to hold the gunwhale, and supports for the 4m long timbers. This worked out pretty well except that I'd already steamed the stb gunwhale into a curve, and half way through the cut the curved length flopped sideways and made the cut a bit deep.
I've temporarily screwed the gunwhale to the hull, using the the long waste piece I trimmed off with the saw to retain a square section to screw through. I used packing tape on the deck, and peeled this off while the glue was still wet to clear up the excess. The G cramp on the end was needed to proved the right amount of twist to match up with the hull.
Phew - gotta do it all again on the port side now !