There's plenty of info on the beowulf mags about legality. Perfectly acceptable, it just happens to accept 223 rds. Just takes a bit of elbow grease, sand and fit, sand and fit. Correction, it does drop free but only on a closed bolt. Have to pull slightly on an open bolt.
I can't see any problems with installing a horizontal charging handle. The oprod spring is fairly weak and doesn't take much to #### it. There's a local outfit who has done the same thing, I've seen and handled one of their jobs. They used a smaller diameter handle and it spins on a rod rather than mine which is stationary. Time will tell.