48" 30515 Snowthrower help needed

I recently purchased the above snow-thrower and I am in need of some help with it. It dates from the late 70's and the picture I have on the manual that I downloaded shows it attached to a Groundsmaster 52. It has been converted to a 3 point hookup and I am looking to change that back to a front mount, but for a Kubota B7100, but that is another story. What I need to know is what speed the two stage impeller should run at. In the 3 point conversion that was made, there was some modification to the drive pulley setup, so I am not sure what speed it was running at. It could have been 540 rpm or some other speed(my Kubota has 3 selectable speeds). I have downloaded the parts catalog and operating instructions but these aren't helping me. Thanks for the input and thanks for the add to your forum.

The simple answer is to hook it to a 3 point PTO and then check the RPM.

I thought of that first but I don't know if the conversion to 3 point kept to the original specs. That's what I really need, the original factory specs for impeller speed. Thanks