This is what I'm finding...

LS1- Weight (lb)* 459 (automatic) 503 (manual)

KA24- ~540 pounds with crossmembers and steering rack attached

SR20DET- 490 lbs with crossmember, tranny and all accessories

RB25DET (aka-fat bastard)- 650LB drivetrain

RB26DETT- cant find, kinda busy and dont remember- anyone?