I have a spindle wizard vmc built on the ex-cello-o 602 base which I am retrofitting right now. I'm just finishing repairing all the broken stuff and switcing to installing the new control. My varispeed housing is probably different than yours but I also have the national 40 tool holders and had looked up the bearings in case the spindle proved bad--thankfully it seems good. The price on those bearings can vary widely so I suggest you shop carefully. I got quoted 280'ish and 300'ish per pair from my supplier of choice (for fafnir) and 520'ish and 380'ish per pair from miller bearing. There's a big difference between $600 vs $1000 to redo your spindle.

I'm going to keep with my varispeed since I have fancy spindle wizard control of the varispeed working but I am also using a 2hp vfd for my 2hp ge motor(easiest way to get 3 phase) and it seems to work well. The vfd unit I'm using is a WEG.