Thanks for all the compliments and words of encouragement guys.
I'm looking into some CFD (Computational Fluid Dynamics) software to try and test not only the VR-4 model but also the "modified" impeller to fit the standard SN scroll cover (we really do need to give that thing a proper name!). The way I look at it, CFD testing will be A LOT cheaper than cutting real parts and keeping my fingers crossed that it does what we all hope.
But I'll keep you all posted as I progress.