I am trying to get some insight into the harness world. I do not know where to really install them etc or what to buy. I want a 3 point and ditch my belts and mount it to the roll cage seems like it would work.Sure looks like it. You could also use the seatbelt mount.
I've never seen a 3 point harness mounted to a mount like the one in your cage though so I can't really comment on that.
Most of the time 3 points are mounted to the seatbelt mounts.
Unless there's a way to remove all the slack in the harness, I don't see it properly mounting to the cage.