That tiller looks great but it is designed to be driven off the tractor from the looks of the pulleys on it. Don't see any corresponding pulleys on the Murray though. These smaller tractors are not like bigger ones with standard 3pt hitches and ptos. I took a tiller that was supposed to be run off my gt14 (a 900# small garden tractor) and put an engine on it to make it self-powered. You could go that direction. I don't know if the Murray is beffy enough to take the pounding the tiller will give. A gear drive would be best on the tractor.
The main drive pulley used for the mower deck may be at the wrong height to allow the drive belt to successfully pass underneath the rear axle. Additionally, the rotation of the main drive pulley may be opposite to that which is needed for the proper rotation of the tines.
I like the idea of adding an additional engine to the tiller, but the added weight and the bouncing around of the tiller maybe too much for your tractor, if it is not specifically designed for it.
Any thought about mounting it on the front of the tractor? The main drive pulley might be more accessible, but the stress is still there..