Does anyone know what a big block with aluminum heads and intake weighs compared to a small block with cast iron intake and heads?

Cast iron intake? Is this a Canadian LG4? All other 3rd gen SBC's got aluminum intakes.

Aluminum heads makes a big difference, but it's still somewhere around 50 pounds heavier than a cast iron SBC.

I have a chance to buy an 83 camaro that has a BBC with aluminum heads and intake, the guy wants 3500 for it but the front end is sitting realy low. I think it needs new springs but the guy insist that the BB does not weigh anymore than the SBC that came out of it. It is a z28 and I do believe it came with a 305 with crossfire injection, was that an aluminum intake?

Yep, that would have had an AL intake.

That BBC is a tad heavier, but more than likely the springs are just 20+ years old and are completely worn out. A new set of 5662 or 5664 (moog, parts store, factory replacement) springs are ~$70 at your favorite autozone or equivalent store - and should set it up right as rain.

Switching from cast iron heads to aluminum heads on a BBC shaves off around 70 pounds at the most. Converting to an aluminum intake might get you 20 more pounds.

Comparing that to a typical cast iron head and intake SBC and the weight isn't much more. On the average, a BBC is 100-150 pounds heavier than a SBC. The extra weight is easily overcome by the torque available from the long stroke BBC.

My car is extremely stripped down but my front axle weight isn't much more than a fully loaded third gen with a SBC. My Dart block is also heavier than a factory block. The bare block is 260 pounds. The tunnel ram is heavier than a single intake and the second carb ads more weight. Just goes to show just how much weight is stripped off my car.