All 10s I have been involved with have 5 forwards and 5 backs.
Odd tourney regs.
I can't see how it's legal to have 3 in the scrum in 10s.
The LoTG are quite clear that the minimum in the scrum has to be 5 each side - unless you're playing 7s.
10s isn't 7s.
5 in the scrum (minimum).
(Wasn't there an incident with this a couple of years back? Wasn't someone injured something and the ref was blamed for allowed a non 5v5 scrum? Or perhaps it was just league points docked or the game replayed. Something anyway..)