well I missed this thread somehow.
Aaron... you mention you're having a clunk or noise while turning? Are the front hubs locked when you're hearing this noise on turns? If the front hubs are locked, the Aussie locker is trying to engage but won't because the t-case isn't locked in. That causes the plates to clack together, making noise but not being able to engage. I generally left the front hubs in "Free" position, until I really needed to go into 4x. This was different than how I've used any previous Bronco over the years, w/out a locker in the front... which I would drive around most of the winter w/hubs locked and ready to engage 4x at a moments notice. It is one short-coming of the Aussie locker... but the flip side is, when you really need it, it's hard to beat the traction a locked front end will give you.
Aussie lockers are very noisy but it's not an indication of a real problem. Read the Aussie info pamphlet included in the booklet I gave you with the Bronco or check the info on their site. For a noise free locker... you'd have to look into spending some serious money for a air or electric lock type locker. The Aussie is the definitive "lunch-box" locker, cheap and noisy but strong and effective.
The motor in question will be the same as any other Ford Bronco 302 with a few exceptions. It was re-manufactured from the Engine Factory in '03. They did use different heads on it and those heads require different spark plugs. If you remove the plugs you have now... take note of the type before replacement. The PO before I bought it had the wrong plugs in it and they would barely seat properly, much less seal. The plugs recommended in Haynes manual were not the right ones either. With some help around here... we finally identified the heads and found the right plugs to use. I did so on the last tune-up and was much happier with the results.
As to the original question about the cold air intake... other than refining the stock setup, I've never really seen anything that impressive around here, like the guys are saying.
You could install hood vents and go with a open cone K&N but you'd still get some engine heat. I have considered that but I like the look and tend to think the added airflow would be great but with the weather in our area, I'd be seriously concerned about moisture on the engine (rain, puddle jumping, etc.) and that's why I never went there... well, that and I don't have money to waste.
A link to my SuperMotors account for your Bronco: 1990 Ford Bronco pictures, photos, videos, and sounds | SuperMotors.net