Coincidently enough I just ordered one, along with a few others I've been meaning get, last night. I had surgery on my right knee yesterday and figured I'll have some time over the next few weeks to put together some easier kits in between Saturn 1B work sessions.
Anyway, to get back on topic, I've taken to leaving room for boosters on the last few clones that I've built (FSI NOVA, Voyager, EOS to name a few) and like Steve thought the Lune R-1 would be a fine candidate as well. As far as an SLS upscale, doesn't Carl make a FSI Black Brant cone?

Sean