All the DET's that we use in b13/14/15's are from awd vehicles (I think, I have heard there are a few fwd one's, but im not sure). The difference between the BB and the GTiR is that the GTiR comes with a T28, has stronger main bolt caps, has individual throttle bodies, and has stronger rods. It also has 8.3:1 cr due to the fact that it has a larger combustion chamber (pistons are the same). There is also the new avenir BB, which I believe has a newer style ball bearing T25. BTW, the blue birds have T25's.
Now, the difference between the US sr20de (what is in your friends se-r, and mine), is this. The usdm has 9.5:1 compression ratio, det has 8.5:1. The DET has oil squiters, a bigger oil pump, and bigger injectors. The S chasis sr20det's (red tops, black tops, etc, from silvia's), have a variable intake cam, and direct ignition, but im not as familier with those. Im not sure of the specs on the turbo's either. I think the newer ones came with ball bearing turbo's also, but dont quote me on that.
The usdm motor can hold plenty of power though. As long as it was maintaned well it can still be turbo'd. The most important thing is to avoid detonation. The two biggest advantages I see of going with a det is the oil piston squirters and lower c/r (good for higher boost on crappy gas). that and you dont have to bother with drilling the block for the oil line.