I don't think you can believe the complete engine weights table.
It says:
SR20DET Complete
+ Five Speed 490lbs (source Sport Compact Car)
L28 complete with stock manifolds, SU's, and A/C compressor + 5 spd 523lbs
The SR20DET is a 4-cylinder aluminum blocked motor probably without A/C
The L28 is a 6 cylinder iron blocked motor.
Yes the SR20DET does have a turbo, but only 33 lbs of difference??? The L28 guys will swear its correct, but the last time I checked, iron weighed about double what aluminum weighed.
I saved more than 33 lbs on my sbc conversion by replacing the iron heads with aluminum ones. One would think that replacing the block with one half as big made of aluminum would save more.
No, I have no empirical data, just observational data.