Hello!
They have messed it up.... the Thunder Tiger .40 PRO SE (and .46 PRO SE) is more powerfull ( hp) than the .42 GP engines.
The PRO SE series engines have ball bearings and larger carb intake and different porting .....most of the time this means more power.
The GP series of engines has a plain bearinged crankshaft, smaller carb intake and not so radical exhaust timing and porting compared to the PRO SE series.

Regards!
Jan K
Sweden