The first post mentioned that these parts are made for Realism Overhaul. But as the sizes and values are mirroring those of the future SLS, I thought it will be adequate for me to use RSS Furthermore, I'll not recommend it, as there are engine performance issue with just RSS (i.e. without RO (didn't try it)). Your mileage may vary (i'll love to hear from someone who's using this mod with RSS) Update : after installing RO, i checked all the SLS related boosters I could put my hand onto. Surprisingly enough ALL of them are off as far as burning time is concerned, even the one provided/modified by RO (!?). Weight, mass, isp, thrust are ok, but burning time falls short about 30s... The core stage is ok, RO or not (very small deviations from real stuff, if at all)