Right, so after some trial and error, I can complete this about 2/3 of the time. Here's what I've learned, wall o' text incoming.
There's 5 threats in this mission. A few infantry, 3 BTR-80s, and a Zu-23. The one that will kill you is the Zu, so go after it first, the rest is just clean-up. From what I've seen it fires 4-5 1s bursts, spaced ~5s apart, and then pauses (reloads?) for 15s. This is when you kill it. At all costs you have to avoid eating a full burst face-on, (or at all) as this will kill your pilots/everything.
Approach #1 involves coming in at 4-5 thousand feet, at average speed. Select rockets, single pair, sight +60 (or whatever you're comfortable with). Keep an eye on the Zu, count its bursts. Dodging the first set should be easy, just weave side to side slowly as you descend. Slow down a bit during it's 15s pause, your going to need to dodge another set and your don't want to overfly.
For its next set of bursts, you'll want to dodge maybe the first 2-3, and then begin your final attack run, keeping in mind you still have 1-2 more bursts coming at you, and if these hit your cockpit you lose. The best way I've found is to come at it sort of like a question mark, with you at the dot, and the Zu at the other end. This lets you fly perpendicular to its firing line as you descend, before turning in to it while it's reloading for the final run. You're going to be dropping really fast during this whole maneuver, finishing with a point-blank rocket to the face. You'll need a very near miss or direct hit to kill it, and if you don't kill it before it reloads, (ie in one run) you lose.
For approach #2, come in at about 4 thousand feet, at max speed. Select rockets, 4-5-pair, experiment with sight settings but I still use +60. Same dodging as the Zu fires its first bursts, but descend somewhat fast as you do. You want to get as close as possible while its firing at you because after that you'll be sniping with rockets. After you've counted 4 bursts, level out and start firing rockets. Fire slow and use the first hits to correct later shots. Fifteen seconds is longer then you think and its a long shot. If you run out of rockets or 15s pass without a kill, you lose, though keep in mind that if you use all your rockets but *do* get the kill, the BTR-80s are quite doable with mini-guns.
I've found sniping with rockets to be a bit easier to pick up, but its mostly a matter of whether your flying (approach 1) or shooting (approach 2) is better.
I've attached two track files demonstrating (more or less) approach #1. Both of them are a bit corrupted but the initial run on the Zu is still fine, after that you'll see me shooting random patches of ground/pilot getting killed when he didn't etc. The one labeled "correct" shows a clean run, the one labeled "ohshit" shows a hilariously bad (but successful) run. Hopefully they run at least mostly right.
G'luck in the skies. Huey Instant Hard Ohshit.trk Huey Instant Hard Correct.trk