My R4 GTL came with the engine, gearbox and drive shafts seperately (plus a lot of other bits). I have fitted one of the drive shafts today and it appears too short as it is not fully into the gearbox. They are 700mm long as in the Der Franzose catalogue.
The splines have not engaged fully in the differential planet gears. Turn the driveshaft slightly when pushing it in ans also rock the inner joint up and down-it needs to be as square as possible to the differential.