My Clubmans are mounted upside down with specially modified Honda 350 risers for 7/8" bars.
A friend with a lathe turned down the Honda to match the Triumph stem size and threads.
This arrangement is an old 'Chopper' trick and is actually a good setup.
Moderate rise and the narrower width makes for a much better handling bike, imho.
'P' Clamps would be work hardened by bending and re-bending, some have bent with heat- neither a good idea.