I have a 2003 GTX SC that I am changing the pump housing to aluminum and putting on a stage one kit from R&D. The tech at R&D told me if my stock impeller is in good shape then use that, which its in excellent shape. He said don't waste your money on a Solas impeller if your stock is good. My question is, am I wasting my money on a stage one kit without the 13/20 impeller Riva stage one kit comes with? Thoughts?