There's 2 problems I could see arising from this. We had an L series at work, I don't remember which model or if it was the same as your tractor but knowing Kubota's "if it ain't broke don't fix it" attitude it's probably a similar setup.
Since the lift cylinder for the quick hitch works off the loader valve you're going to have to disconnect it. This is where you may discover the cylinder slightly leaks internally and the frame lowers itself overtime with no way to pick it back up since it's not connected to the tractor hydraulics. This could likely be overcome fairly easily with a ratchet strap but it's another thing to worry about.
The more likely issue is the loader hitting the quick hitch when lowered since it sticks out basically right into where the crossbar is. It may clear it, it may not. You'll have to measure it and see.
If it does clear the loader then it SHOULD work provided you can tie up the extra hydraulic hoses in such a way that they won't catch on anything and keep the hitch from moving on its own. If the loader mounts can stay on with the sub frame then you're really not adding anything that would interfere by putting the loader back on other than the possible collision between the loader crossbar and the hitch. You might just have to try it and see.
