Have a look at the Gazaile 2 by Serge Pennec. Its not an SSDR but it uses the mechanically injected 1400cc diesel used in the Citroen AX, early Peugeot 106, Citroen Saxo and Rover Metro 1.4D.
Gaz'aile 2 : english informations
You would need a light airframe to carry the extra weight of a diesel, but it could be done with a weightshift or paramotor trike.
The beauty of this engine is that its designed for long autoroute cruising at near flat out, which larger diesels may not be. It is also a lot simpler than later common rail engines.
If I remember correctly the Gazaile predecessor the Dieselis, used the Isuzu 1.5 turbodiesel found in the early Vauxhall & Opel Corsa B.
http://gazaile2.free.fr/diesel.php
If your French isn't great, just and past the text into Google translate.
You could look at the 505cc Lombardini diesels used in Microcars, although they would need some serious tweaking (turbocharging?) to get a decent power to weight ratio.
I'm sure I have seen diesel trikes in French microlight magazines, although they may have been over SSDR weight.
Here is a converted Smart Car diesel engine:
FlyEco - Innovative Drives for Ultralights
To get best power to weight you need high revs, and for best efficiency you want a big propeller. To get both you need a reduction drive, and for that to survive the torque reversals at low rpms you really need a torque limiting clutch, which is extra weight.
More on the Smart diesel here:
http://www.microlighters.co.za/viewt...113f22b3232fb1