Comng from a track racing background, I have NEVER used a lockring, even on the road. Back in the 70's, my first track coach, an ex-Euro-6-day pro, told us never to backpedal to slow down. On the track, it's too sudden. (You control speed by using the banking.) So if you're using a road frame with 120 rear spacing, just center the old-style threaded road hub so you don't need to dish the wheel (which may require redishing to center the rim), insert a 2mm spacer and then the track cog (to get the chainline), and just make sure you tighten the cog with a chain whip (or a real cog remover if you're really cool). If you have 126 spacing and a 126 hub, good luck. You will find that the axle length is too long to support riders over 170 lbs, and you'll end up breaking axles. This is why they went to cassettes.

I think skid stops are stupid. I've been riding fixed for over 40 years and have never needed to backpedal; the brakes work way better (or on the track you just float until you come to a gradual stop). If the chain falls off on a descent and gets caught, the cog merely unthreads. If it's secured with a lock ring, the rear wheel locks up and now you've got to control some serious fish-tailing. If you ever watch those videos of tandems crashing on the track, it's due to using lock rings!

If you really must do skid stops, then get a real track hub with a real lock ring. A bottom bracket lock ring will fit a threaded freewheel hub, but you will find that both cog and lockring unthread together. This is why they invented reverse-threaded stepped lockrings.

Luis