Nice lookin' car, but here's the deal on converting from The Lean Burn system.
Disclaimer- It may not even be legal in your state, since it's considered "tampering" with your emissions system. Check your local laws.
It's not just a matter of putting on a different carb. A different carb (and intake manifold, I presume) will no longer give the computer the inputs it needs in order to control the ignition timing and advance. Yes, it has rudimentary ignition control, it's that box on the air cleaner horn. But you can't just take off the Lean Burn box, since the Lean Burn distributor has no vacuum advance of it's own, and the box is now missing to control spark.
What this adds up to is this:
Remove intake, carburetor and linkage; along with air cleaner/control box.
Remove distributor.
Install one of the many MP/DC type electronic conversion packages that are available. These kits include the distributor, coil, ballast, control box, and wiring. Yes, wiring. You'll need to get a FSM with wiring diagrams for your particular car and start tracing wires, splicing in the correct wires at the correct locations, and eliminating sections that are no longer needed. Basically, you just need to find power feeds for the Ignition start (NOT the starter circuit) and ignition run.
Install the carburetor/intake manifold of your choice. You will most likely need different throttle and transmission kickdown linkage bits and brackets to get everything hooked up. You'll also need to bend up some fuel lines and add a filter. Oil pressure and coolant sensors *should* remain the same IIRC, as well as the alternator VR circuit; I won't swear to the VR circuit but I'm pretty sure. Top it off with a new air cleaner of your choice.
Once you get the correct carb linkage on it, transmission (an A999, BTW) control should not be an issue- the lockup in those years is completely hydraulically controlled and will remain functional.
You didn't mention what performance mods you have in mind, but I also assume you'll want to get rid of the single exhaust and catalytic convertor. Did you want to just run duals from your stock manifolds? Guess what- you've got an air pump and air injection lines to contend with- you'll need to remove the pump, bracketry, and injection lines that go to the manifolds; and then plug or otherwise block off where the connections were in the manifolds. Well, I'll just put headers on it, you say? Once the manifolds are removed, there are eight air injection ports directly below the exhaust ports that need to be tapped and plugged with allen screws to prevent what would amount to an enormous exhaust leak.
All this will get you a four-barrel and free flowing exhaust, but still leaves you with the stock cam, which honestly isn't bad for a stocker; the LA roller cams (which is what you have) aren't horrible, just nothing special. (BTW, aftermarket cam blanks for these motors are a little hard to find at the moment- but not impossible).
Welcome to the rabbit hole.
Edit: I take back that bit about the roller lifters- you've got hydraulic flat tappets. Rollers didn't start until '84 or so, I believe. Sorry for the confusion.