Remember the other 3 cylinder National that was on ebay? I managed to get in touch with Steve who bought it, and now he has a blog to record its rebuild. Good luck with the engine Steve - but whatever happens, don't stop the blog! There are already some lovely photos linked from Steve's blog, and we've enjoyed poring over them spotting the similarities and differences.
Steve's is a D3, whereas Warrior's is a DM3, the difference being the M for marine. Basically, it looks very similar, but it's the peripherals that make the difference. I've seen one other like it (in a shed), as well as a few D2s and DM2s in boats.
The other 3 cylinder National that we'd heard of already installed in a boat turns out to be a DA3, similar to Hadar's DA2. This is quite a different looking engine, from the photos I've seen, although I've yet to see one in the flesh.
I've added Steve's blog to the blogroll, along with Diamond Geezer (highly recommended) and Newhaven Town (so called because that is the name of one of its three railway stations).