Yeah, spinning right on to rails is tough... I tried it once on to a right-curving C Box because I felt it would be easier to slide it facing away from the ground and instantly annihilated myself. It should, in theory, be easier to maintain balance once you land though because you slide right foot first. It just requires you to execute and commit to a 270 right-side spin. I think the idea of progressing from 90, to 180, to 270 is a good one. I can slide unnatty no problem doing a regular (left-side) 270 on, but sliding unnatty by doing a right-side 90 on fucks my shit up way more because of the right-side spin, so building up to it sounds promising.