i want to save gas on my 350 motor?

If the engine is in good tune about the only thing you can do is go easy on acceleration especially if this is a 4 barrel carb. Heavy on the accelerator makes the secondaries open in the carb, using more gas.

Reduce vehicle weight, inflate tires to proper level, change fluids at recommended intervals, slow down, and accelerate/drive smoothly (most can't figure out how to keep a steady pedal anymore)

If the carb is not tuned correctly, fix that.

Outside of those, a big heavy car, with a 5.7L old technology motor, is going to use a lot of fuel. Even with overdrive and fuel injection, those engines did well to see low 20's for MPG. This is why the 305 was developed, even if it wasn't as good in execution as it was in theory.

If you don't believe that economy is tied to the factors I say it is, what do all economy cars share in common...light weight, thin tires, tiny motors.

Well it depends on how the motor is set-up. I would start with a good tune-up and setting the timing also tuning the carburetor would help you may need to change to the right size and type of carburetor. A lot of people have this idea that putting a bigger carb on makes it work better or more power but it hurts the cars performance buy flooding the engine.

You're best bet is to take it to an experienced speed shop and let them use an exhaust sniffer to tune the carb for best performance. A little higher octane fuel might help. Some STP oil treatment once a year could make a bit of difference too.

Don't drive it hard or you could change the intake and carb. That motor stock only got about 13 mpg anyway. The only things that would increase milage would be go back to the original 6 cylinder or modern feul injection.

Amsoil P.I. is great for fuel effeciency. It cleans your carb and internals. So far its the best ive seen for getting the best results.

It pretty well is what it is. You can make sure it's tuned but nothing you do is going to make a big noticeable difference.