The best way is to have the prop washer and the prop nut that came with the engine. Scratch that, I just looked up the engine and it comes with what you already have so everyone knows, here is a pic of it.

I would do the LHS first. It will be more expensive but it will be a better match.

I'm a little short on time or I would do it for you, but a little research may yield someone that has the correct prop nut/washer combo

Here is where I found the picture. It shows the shaft size. Now that I have looked it appears from re-reading your posts that you did do some homework. Cool stuff. I did a very quick look at the recommended lists of items for this engine and it seems you are dead on.

http://www.hobbypeople.net/gallery/211300.asp (there are other places but I'm a little short on time)

I'll be back later to check this out and if no one has posted about finding or not finding a prop nut for you I'll dig a little deeper.