A passenger weighs more than the weight difference of the engines.
With alum heads, the difference shrinks.
Front suspension really doesn't require any changes to support a bit more weight. A re-alignment and adjustment of the torsion bars usually works fine. I know my car doesn't dip much when I stand on the bumper, and I weigh far more than the difference between a SB and a BB.
If it were me, comparing putting alum heads on a SB vs putting headers on a BB, I'd be going with the BB and still looking at alum heads. Sell a few SB intakes to fund a BB intake and it's a wash other than the headers, oil pan, and distributor. It's also helpful that the SB is already in the car, keeping it driveable while the new BB setup is being assembled, which means time can be taken to find deals on used parts rather than paying full retail to assemble.
This is how I look at it, at least.
