Outfitter
Outfitter is an excellent workshop addon that allows players to load any playermodel from the workhop in-game. The server doesn't require the content.

With Outfitter, players just see their legs represented as their last applied vanilla model using gmod's player model selector. I think the issue is that the legs mod is referencing server content for player models and I'm not entirely sure if Outfitter installs the player model addons server-side or if it's just client-side.

I also contacted the outfitter devs regarding this: Issue[github.com]

Either way I would love to see Legs3 become compatible with Outfitter.