If anybody else is thinking of buying a model of the merlin, the best one (don't know about the mk3 version) if you can call it the best is the revell as extra required parts are included, such as weapons carriers, sonar chute (flattish disc), HF aerial, rear view mirrors (that wouldn't be out of place on a huge truck) better decals. In general the revell version has more to offer, but with still a hell of a lot of faults. If resin and photoetch parts were produced to do this model justice, then the company that made them would certainly make a killing.
If you want any pointers on these kits I'll try and help (not the best builder in the world, but I thoroughly enjoyed the build and looking at my end results. Here is a Seaking MK6 I built quite a few years ago