Only you can decide if it's a good idea but here a some things to think about:
1. The Kohler can be rebuilt to new specs for $500 or less if you do the work.
2. You will never get your money out of the tractor if you put a different engine in it.
3. The Kubota will require some modification of the hood to make more room and it will not look stock.
4. If the diesel operating speed is not close to 3600 rpm then you will have to install a different pump to maintain adequate gpm.
5. You will need to do some special fabrication to install a front PTO assuming there is a way to attach it to the flywheel.
6. If you don't have a front PTO you will not be able to take full advantage of the power of the diesel.
All of these issues can be dealt with if you have the skill and you could end up with a real brute of a tractor. Ingersoll actually sold a diesel for a couple of years and you can download the parts manual and see how they did it. The main thing they did was extend the front of the tractor frame to make room for a radiator and that required a longer hood. They also dispensed with the mechanical front PTO in favor of all hydraulic driven attachments.
1. The Kohler can be rebuilt to new specs for $500 or less if you do the work.
2. You will never get your money out of the tractor if you put a different engine in it.
3. The Kubota will require some modification of the hood to make more room and it will not look stock.
4. If the diesel operating speed is not close to 3600 rpm then you will have to install a different pump to maintain adequate gpm.
5. You will need to do some special fabrication to install a front PTO assuming there is a way to attach it to the flywheel.
6. If you don't have a front PTO you will not be able to take full advantage of the power of the diesel.
All of these issues can be dealt with if you have the skill and you could end up with a real brute of a tractor. Ingersoll actually sold a diesel for a couple of years and you can download the parts manual and see how they did it. The main thing they did was extend the front of the tractor frame to make room for a radiator and that required a longer hood. They also dispensed with the mechanical front PTO in favor of all hydraulic driven attachments.