you can achieve better weight distribution by putting a SR into a r32. the engine bay is designed for a inline 6 so the front axles sit further from the firewall (or the firewall sits further back from the front axles, whichever way you want to put it). so by using the sr20, you get the advantage of almost a mid engined car as most of the engine sits behind the front axle.
yes the gtr is a 1400kg car, but only because of the heavy 4wd system and the iron block inline 6. drop a alloy block sr20 and ditching the 4wd system, you could get the weight right down.
the sr20 has had a lot of development as well and big useable power can be obtained.