that setup is kinda wack.
using a GSR ecu on a b16 head/IM with no IAB's is counter-productive....
IMO, if you're looking to buy this car used from someone, i'd re-think your offer. sounds like a hack-job.
as for the tranny,
the closer the gearing, the faster the car will accelerate.
the longer the gearing, the slower the car will accelerate.
LS is the longest tranny for b-series.
you do the math.