I have an old WG unit but the only thing left from that is the DI cartridges and the metal plate. The membrane is a SpectraPure 98% and greater membrane, and pre-filters from BFS and BRS and DI from SpectraPure.
The filters and membrane are standard ones. No matter what else you do, get the high rejection membrane from SP, in old house incoming tds was about 300 and it took it to 1 before the DI, new house has a tds of 230 and it takes it to 0-1 before the DI. I also get better life out of SP's DI resin.