Point number one: if the model is to represent a ship of William the Conqueror's fleet, as Heller intended, any reference to the Vikings is irrelevant. William the Conqueror was not a Viking.
I think the premise Heller used for this kit was simply that the ships in the Bayeux Tapestry (the one great contemporary visual representation of the Norman Conquest of England) look vaguely like Viking ships, so a kit representing a Viking ship (the Heller "Drakkar Oseberg," which, as we covered earlier in this forum, is in fact a lousy replica of the Oseberg Ship) would, with some minor modifications, work. Since the kit does such a poor job of depicting a Viking ship, I suppose it can represent a ship from the Bayeux Tapestry just as well.
Anyway, the Bayeux Tapestry does show shields hanging on the sides of the ships (though it doesn't show the means of fastening them there). The various books on the Viking ships (try The Viking, published by the Tre Trekare firm, and Bjorn Landstrom's old classic The Ship) have good representations of how the Vikings hung shields on the gunwales. (I'd have to get out one of the drawings, but as I recall there's a narrow strip of wood with slits in it nailed inside the gunwales and the leather straps on the backs of the shields go through the slits.) I imagine William's ships used some similar system.
One of the most common - and eroneous - assumptions that people make in reconstructing historical stuff is that our ancestors didn't like bright colors. Such evidence as we have suggests that, in fact, their tastes in color were pretty bold. The Greeks originally painted the friezes around the roof of the Parthenon in brilliant colors. And recent research has indicated that Victorian houses, which we so often think of as being painted white or various subtle pastel shades, often were alarming shades of green, blue, purple, and pink. Over the years several housepaint companies have manufactured ranges of "Authentic Williamsburg Colors" that, they claim, are exact reproductions of eighteenth-century paint samples found at Colonial Williamsburg. The colors are accurate, all right - they're accurate duplicates of paint that's been fading for over a century.
My suggestion is to take a careful look at a good reproduction of the Bayeux Tapestry (plenty of photos of it are available in books and magazines - and probably on the web), and take into account the effect that a thousand years of age and light have had on the colors. I suspect those old ships originally looked pretty spectacular.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.