The GR2 is new and has not been reviewed. I have not heard it. My comments must be interpolated by you and I hope they help. I had a fully KAB upgraded SL1200, which I am assuming is similar to yours. When the new SL-1200GAE came out I traded for one. The GAE in terms of form, fit and function is pretty much a match for the current G. So it is twice the price of the GR2 that you are looking at. Looking at my notes from back when I made the trade, the GAE was an improvement over the KAB SL1200, but the differences were subtle. There was slightly greater clarity particularly in the upper mids, for example on piano that I attributed to the arm. The arm of the GAE/G is magnesium. The arm on both the KAB/SL1200 and on the GR2 are aluminum. You need to reflect on that fact. I could detect no cogging from either tt, nor could I really detect any significant differences in speed stability, wow & flutter and the like. The GAE was better, but not by leaps and bounds. My guess is that a GR2 and your KAB modded unit would be very similar in performance.
Regards,
Bill