Throttle Body vs Carb Spacer

[Foxtrot]

I don't think I understand the basic difference between a throttle and carburetor. Isn't the throttle just a part within the carburetor-the valve itself that actually controls fuel flow while the carb is responsible more for the airflow and mixing the fuel?

I've been doing research on improving the economy of my truck. One suggestion is to add a throttle body spacer. I started looking into these for my model, and found there were none, but was something called a carburetor spacer instead. Did further research, and I'm just kinda stumped. What's the difference between the two, and for my MKIV ('79) Big Block, which do I actually need?

Assuming a carb spacer is what I'm after... From what I have learned, the carb spacer has two purposes: keeping the carb cooler and allowing more air volume/atomization/less resistance. As such, a plastic 2" carb spacer would be better at doing its job than an aluminum 1" spacer? More volume and less heat conductivity?

Again, for reference, I have a 1979 C20 Camper Special (Silverado) with a 454--all original.