[weight nazi ]with an auto trans and all the wiring and accesaries and stuff a full up LS1 is supposed to weigh about 150lbs less than an iron headed gen 1 small block(basically comparied to a complete f-bdoy L98)
another nice thing about the LS1 is that the motor moutn positioning and lack of a dist allow it to sit 3/4 inch lower and 2inches farther back in the car.

[/weight nazi]
later
tim