well, if anyone is to attempt this, which i doubt, but still.
I tried to interchange necks between RGA321 and RG2120X(i blocked the trem).
i considered there could be intonation problems, but they actually don't fit. first of all, the Ultra neck is 1mm narrower, but okay.
Secondly, neck holes don't line up (that surprised me, since they do for the 7stringers).
looks like the only thing is to get a custom neck.
i just love my "velvet touch" ultra neck so much

it just feels so better.
anyway, how can you succesfully strip the
neck finish, from the wood grain also?