Without a license, we're allowed 6ftlb for pistols and 12ftlb for rifles.
There's a lot of different opinions where converted pistols are concerned - the law surrounding it is a grey area so, no one really knows for sure.
My belief is that a court would see a pistol as being able to be fired from 1 or 2 hands, arms out stretched and, a rifle as requiring 3 points of contact, shouldered.
So, if a pistol is converted to have a longer barrel and a fixed butt, I'd be happy to up the power to 12ftlb.