I know that the QG18 in the b15 sentras have the 4.1 final and is a direct swap over. The bell housing half is the only thing that will have to be swapped over from the sr20 70a. Not sure about the...
The passenger (RH) side engine mount will cause the most vibration and noise in the cabin. Try replacing it with an OEM mount and see how the car feels.
Im going with hydraulic on my N14. Ive got 70A for 90USD and it came with slave cylinder too so I need only few parts to make it complete. I think that N16 pedal and master cylinder should fit N14.
same idea with lowering springs. a stiffer spring will exert more force upon compression so it does not have to be the same length as oem. run it and gun it, bud.