Thinking of upgrading the stock Air Cleaner?
Cold Air Intake
Cold air is very important. Instead of hot underhood air, bring in cooler fresh air from outside. It makes a big difference, and is a nearly free -- no "intercooler" needed.
Lynx Ramflo open element
This supposedly lets the engine breathe with less restriction, and therefore gives you one to two additional horsepower.
Ram air. Use a mini-shaker hood scoop. Plumb it to the carb. Not only will it bring in cool, dense outside air, but the scoop shakes at idle. Cool!
Vanette Air Cleaner
Nissan Vanette with A-series engine uses a Hitachi carburetor top-hat and a remote air cleaner.