If my memory serves me, aren't most 2 stroke diesel's turbocharged? Other than the obvious reason for a turbo (more air=more fuel=more power) they also allow you to run an ohv system.
So I guess you will be running a conventional 2 stroke (ported cylinger walls). If you are going this way may I suggest you start with a rotax 670 bottom end. These engines have a reputation for taking big power upgrades, and living. I think they were rated at about 120hp stock, and with big bore kits, and NOx would make double that. So at a rating of 70-100hp, (granted there will be more torque than a gas engine) you will have a proven, aluminum 2 stroke bottom end. Then, for the prototype, you will have less to deal with, and that may allow you to focus on the fuel system.
I'd skip the mechanical injection, and go straight to a common rail electronic. This will allow you to tailor the fuel curve in your air cooled engine to keep EGT's under control. Have you also considered a cooling system for the return fuel? I only mention this because on a 100hp aircraft you probably have a small fuel tank, and the whole engine will be running on the hot side, thus heating up your return fuel more than it would be on a 100hp water cooled.
This looks like an interesting project.