[Jonboy]

Another easy way to tell is that on the B body (Roadmaster, Caprice/Impala SS, Fleetwood) cars, the LT1 cars have dual exhaust. There is a 4.3 V8 (L99 I think) that looks identical, but is pretty much useless for performance. The B body LT1's are similar to the F (Camaro/Firebird) and Y (Corvette) engines, with the exception of the heads. B car engines are rated at 260 HP, and have iron heads. The F car engine is rated at 275 HP, and the Y car is 300. The only differences in the F & Y engines are the intake and exhaust packaging (and accessory drives), with the F car being a lot tighter to fit in the space.