The main thing is to get a good running tractor with good tracks and undercarriage.
For desirable features, there's the oil clutch which I doubt is as important on a D2 as on a larger tractor, but should (almost completely) eliminate clutch replacement worries.
Then there are 5 roller track frames which would help when trying to doze something flat without the speed bumps.
Then the rest is just getting one equipped with the dozer, hydraulics, winch, pto etc you want. Usually getting these when you buy the machine is the cheapest/easiest you will ever get them. Trying to run them down later and install them can be frustrating.
A D2 isn't the easiest tractor in the world to fix steering clutches etc on. The components are lighter than the larger tractors, but for instance, steering clutches/brakes that can be removed as a unit on the larger tractors require breaking the tracks and removing the track frames and final drives to remove from a D2
D2-5J's, D6-9U's, D318 and D333 power units, 12E-99E grader, 922B & 944A wheel loaders, D330C generator set, DW20 water tanker and a bunch of Jersey cows to take care of in my spare time๐