This is from an interview on the Quins site.
This shows that the only difference is who feeds the scrum, after that the two half backs operate on opposite sides. One half back on each side of the ruck area.Interviewer
Will it be 6 or 7?
Danny Orr
It doesn't make much difference these days. I usually wear 6, but 7 puts the ball in the scrum, that's the only difference
Interviewer
First or second Receiver, or left and right of the ruck?
Danny Orr
Brian's not yet worked with us on that.
It's a sad fact, that the 10 yard rule has changed the game to the point that two specialist positions have merged in to one. It's just like having two wingers, or 2 props.
When we had the 5 yard rule, scrum halves had to be clever if they wanted to unlock defences. Attacking lines had to be deeper. All it is now is fitness and speed. We will never produce another Andy greg or Alex Murphy, the game isn't played in a way that would suit them.