I find LeftScalar and DRight strangely inconsistent (Left as a prefix and Right as a postfix).  Also, if you believe in long names, D is not very nice.

I think that Left/Right is not the important part of the name, so I'd be fine with abbreviating to L/R.  D, on the other hand, could be usefully expanded to Dimensions (is that what it means?).

So my vote would be for LScalar and RDimension or some such (but arguably that's bikeshedding).