Well it can be if I want it. Right now I did few variants like this, as I want to be able to put it on stock tamiya euro trucks, and driveshaft goes over battery box, so if I put rear output on the bottom, I will have to remove the battery from stock position. But yeah, its easy to make the output front/rear one the same lower shaft if someone needs it like that. But this design will be easier to put clutch on it, to disconnect front drive when wanted, or when in 2. and 3. gear. I will try to work out a way to use stock gearbox gear selector, to engage front drive only in 1. gear. But first I need to test the design in reality. US style trucks have enough space so it will fit on them without problems.
The above design is not really what I wanted for my build, today I did a new version that sits more on the side, so I have a straight driveshaft for my front axle.
First prototype, this is harder to install. First GRU was 2min job, but for this, few truck parts will have to be removed to be able to install it. And I think I will have to modify battery tray as there is not enough space.