Power Steering fluid type/brand and air filter model# help

Hi All,
I have just purchased a 1973 Dodge Dart Swinger and I need to replenish the power steering fluid as it 's low....Looking for best brand/type to use as I haven't had the need previously to hunt down correct fluids for a classic car......Also the car had a /6 in it and now has a 318 with a dual snorkel air filter. Is this possibly a component from a 318 truck motor setup?...I measured the inside circumference of where the air filter would sit and it looks like 10 3/4...but can't seem to find air filter to fit...318 car filters seem to only measure 10"...Any thoughts? Please see picture below...Thanks as always for your assistance...Greg