#1... L-series oil pumps are quite hefty. If you are experiencing "low oil pressure" check the oil (level, and cleanliness) first, then check the oil pressure sensor. The sensor is much more common to produce a faulty signal, than for an oil pump to "pump" low pressure. I had a 280zx that would bearly register oil pressure on the gauge... swapped sensors... ka-blam-o... good oil pressure.
#2... Any L-series clutch assembly will work on any L-series motor. BUT... the 280zxt and all 280zx 2+2's have the larger 240mm flywheel... so... use the 240mm flywheel.
#3... Any L-series tranny will bolt up to any L-series motor. NO... A Mustang / Camaro T5 will NOT bolt right up, as it is not designed for an L-series motor.