I have seen some billet spacers/adapters over the years. I would assume they need to have torque checked also, but do you think they would be better than the ones that look like they are made out of cast pot metal?
I made my own spacers when I was working. Steel on one car, billet 6061 at a half inch thick on another. Both drilled to fit nicely on the axle hub. 3 in screw-in studs in one car, 3in spline studs on the other.
I would not use the cast aluminum spacers with 15 or 20 lug holes in them.
I check torque on them before every race.