The LS1 is a great swap because it's light years ahead of the gen2 SBC. It is about 150lbs lighter, produces lots of clean horsepower and gets great mileage. Also, the seals and gaskets are precision and are designed not to leak.
1991 Formula Firebird
2001 LS1/4L60E, 3.23 posi rear
Comp XE 216/216 .577/.577 114LSA cam
918 Springs, hardened pushrods
Yank SS3600 torque converter
PCM reprogrammed for cam and converter
3" exhaust
BRM Adjustable torque arm, tubular read LCAs
Spohn Adjustable panhard bar, front steering brace
Spohn Subframe Connectors
4th Gen style wheels
Bilsteins sport struts and shocks