I can't vouch for anything, as the extent of my SKX modding is putting in a lumed bezel insert (then leaving it in a drawer because i find I don't really like the SKX) but The Urban Gentry on youtube has a really nice modded SKX that he got from
https://www.instagram.com/watchmakers4/
video of unboxing (skip ahead to around 5:00 to avoid the "nonsense"
Northeast Watch Works is another I've read positive reviews about.
www.newatchworks.com