Swing blade gearbox.

[Grower]

Hello, I am looking at building a swing blade mill but want to ask about gearboxes. I am attaching a photo of one I have on hand (I have 3 but want to focus on this one), it is off a piece of agricultural machinery that was scuttled for parts some time ago. The input shaft runs at 540rpm (a standard PTO speed) and the box is rated approx 35hp (it could be 40hp I do not have the owners manual on hand but the machine was used for a number of years on the farm by me), the input shaft runs at a ratio of 4:3 (3 being the output), I want to know if it can be run in reverse at 2400 rpm input speed via a diesel engine to get an output speed of 3,000 rpm to run the blade at. What would be the consequences, if any?