No those are angular contact and have silicon nitride balls, specs here
s608cta.pdf
In fact i will fit them on Monday i hope and see how they perform.
I tried to fit one on the compressor side but it won't fit in the shaft tunnel and it is getting stuck rendering preload useless.
I will try to enlarge a bit the shaft tunnel a i plan to replace it with an iron one.
UPDATE:
I used the dremel tool and some polishing compound and now i can se my self inside the shaft tunnel, that shine removed just enough material to make the GMN bearings slide nicely in.
The GMN bearings had 2 hundred of a mm larger outer diameter (22,00 mm instead of 21,98 of the GRW bearings.
Chris