Are you sure it needs overhauled? Unless it starts hard (needs a sniff of ether to start in the summer) or burns lots of oil (quart every 30 hours) it might need injectors.
First of all, replace the inner and outer air filter elements. Replace all the fuel filters and fill then with John Deere fuel conditioner instead of fuel to prime the system. I suggest buying a gallon of the conditioner ($35?), fill the filters, and dump the rest in the tank.
Also, look at the exhaust stack and manifold. If there is oily residue on the joints of the exhaust system after the turbocharger and no oily residue on the manifold where it bolts to the head, look carefully at the turbocharger. Remove the intake boot from the turbo and spin the impeller by hand, making sure it spins free. Check the impeller for end play (in and out movement)--there should be VERY little. There will be a little play up and down--this is normal because this is the space the oil occupies when the turbo is spinning while the engine is running.
Now, back to the injectors. If the turbo checks out and the fuel conditioner and filter change does not help, you need to test the compression. If the compression is low, chances are that it is overhaul time. If the compressions is good, it might be time for a set of injectors. The 4045 engine uses pencil injectors, which are fairly easy to change.
Good luck and don't let anyone talk you into an overhaul without doing a compression test first.