Wow, nice ship! You should try sending it to explore Eve. Also, using radioactive material as ballast is one of the most Kerbal things I've seen done in a while.
Thanks so much for this mod! For some reason the stock method of resource transfer doesn't work for me as of 1.0.5, so I am using this as a substitute. It works great!
I think it just comes with realism overhaul, as part of the pack. Not sure which mod, but it might be the actual RO mod itself.
Edit - You could download RO, then find it in the gamedata, and copy it over to whatever install you want it on.
476 parts is hardly low count. Maybe for you, but I have a potato with 2 gigs of ram shared with the graphics card, and I can't even handle 150 too well. I love the craft though!