I've read that you can run them as either front or rear- specifically a freewheel rear as a front. What do you need to convert the wheel to do this, and where can you get the parts? Also, if ran as a back, is there room for a lockring? Thanks.

You can run a front as a track rear or vice versa, but you can't run a cassette rear as a front or a track rear.

In order to do this you'd need the track axle kit here: https://www.hedcycling.com/cart/accessories.php

The set I have (old ones that say specialized on them) are identical, and you use a different axle for the front and rear. They're both threaded for a cassette, and to use on a fixed gear you screw on a track adapter and then thread the cog onto that. They can't take a lockring though -- the adapter covers up all the threads, so even if you could put one outside the cog you'd just unscrew the adapter. It's not a problem on the track, but you probably don't want to use one on the road without a lockring.

So if I got a rear wheel I could purchase a front axle and run it as a front, or no?

probably, unless there's been some kind of design changes. I bet you can call HED and they would even tell you for sure.