Horsepower on displayed on tractors is somewhat arbitrary. Can be engine gross horsepower or engine net horsepower, or something else. Kubota uses engine net horsepower. Model numbers must not duplicate model designations trademarked by other producers.
The number you should consider for PTO powered implements is PTO horsepower, the actual dyno measured powered at the tractor PTO splines after losses in the drive train on one representative tractor. Individual tractors may vary over published number 1-2 horsepower when new, perhaps adding another horsepower when broken in, then slowly declining as hundreds of engine hours are accumulated.
An exception are the ~~100 cubic inch <25.4794 horsepower tractors which have power reduced below the threshold to avoid Tier IV emission controls. Those had better test below the threshold or manufacturer can be fined billions of dollars, as VW found to its chagrin.