Good news, HG freewheel nut and casette on 600 hub installed. After study of many shimano docsheets, i went around a nice bicycle shop where they gave me an whole old mtb rear wheel for free (what a nice experience.. it was dirty as hell , but.. otherwise they would throw it away..) The hub which i robbed was FHRM40 hub with a Y-3SL98030 fw body. (there is more options as i learned from docsheets, but this one run across, so..) I tought that newermind its 8cog body, i would have room for spacers to adjust it to index shifting, but then, installed chain, and what a surprise, its working with old indexed 600ex shifter without any change on new HG casette. It has similar sound like on my old MTB bike (i could robb the 7cog hub from that bike than i realised.. but no way, that one should stay intact )

..dont care about the gap between 28T (last cog) and spokes.. thats ok, the chain is not jumping inbetween.. There is now still place for 8th cog if i choose to.. (than with friction shifting).
here it is: