i dont see the point on why you would get another GA16.
yes the SR20 would bolt in but you would need a couple other things as well(SR20 radiator and hoses, transmission, axles, ECU, ECU harness, motor mounts, starter. i might be missing some stuff)
and if you do go SR20, get the SR20VE. it has 187WHP stock compared to the 140somethin of the DE.
the VE is also more rev-happy, you can rev it easily up to 8200RPM without the rev limiter.
and last but not least(at all) the VE has NEO-VVL(Nissan Ecologicaly Oriented Variable Valve Lift) which is just nissans version of hondas V-TEC.
ive seen people rev all the way up to 10,000RPM with just porting and new valvetrain and a GOOD tune.
and also the the sr20ve sounds a LOT better:
http://www.youtube.com/watch?v=Y2u-um-v ... re=related