Build Sheets?

Yay! Another 86 2.3L!! I can tell you basically ANYTHING about the powertrain in your car you would want to know. To answer your above questions:

Your car would have a 3.08:1 rear in it unless it has an optional 3.45:1 rear, which is unlikely. The transmission is the German ET with the following gear ratios:
1st 3.98:1
2nd 2.14:1
3rd 1.42:1
4th 1:1
Rev 3.99:1

As carburetors go, your YFA is computer controlled, along with your ignition system. If you do replace the YFA with a different carburetor, the ECU will lose the input of the idle tracking switch and throttle position sensor and lose the output of the fuel control solenoid and idle motor. This will cause the ECU to go into fail-safe mode and lock your ignition timing at 10A, killing your power and fuel economy. That being said, if you switch carburetors (I don't recommend the 2150, I'll explain.) you have to get rid of the entire computer system. Which actually is REALLY easy. Remove the computer and harness and take out the EEC IV distributor. GO get a distributor for a 1979-1982 2.3L mustang or capri. It is the magnetic pickup, vacuum advance Duraspark type. Then you can either wire up a Duraspark box or an MSD box using a very minimum of splices and new wiring. As for a carb, I would use a 2 barrel from a 1977-1982 Mustang, Capri, Pinto, Bobcat, or any Ford 2.3L passenger car. It is called the Motorcraft 5200. It is actually a Weber DFEV (Carb even says Weber inside the fuel bowl) modified by Holley for Ford. Works awesome and comes pre-tuned for the 2.3L! Just be careful not to get a Motorcraft 6500, which is a computer controlled version of the 5200. They can be identified by having a small vacuum line entering the carb right to the left of the fuel inlet. You will also need the 5200 intake spacer. But it all bolts right up. I did this conversion on my Capri and have been very happy with the result. If you have more questions, feel free to contact me. I've got lots of info.

I think the 2150 is the standard Holley pattern so you would have to go to esslinger or racer walsh and get an adapter to fit it to your intake properly. You would lose your EGR system at that point as all the adapters take the place of the current adapter/egr plate that is there. As for the cam being retarded 12-14, that would make a MASSIVE difference in how it runs. In fact, most of the time if the cam is off a tooth, the car won't run. I would double check that it is in fact off a tooth, and if it is, fix that problem BEFORE you do anything else to the engine. Like I said though, if it is truly off a tooth, it would barely run or not at all. Lastly, your fan switch is located in the heater core pipe coming out of the thermostat housing. It should be in a short section of metal pipe almost directly under the plastic part of your intake duct. It has 1 wire (yellow and red I believe) leading to it. Be sure you ask at the parts store for the fan SWITCH and not a sender or sensor as your car has both of those as well (sender is threaded into the driver's side rear of the block and makes the temperature gauge work and the sensor is threaded into the intake near where the coolant line connects in and sends a signal to the ECU). If replacing the switch does not do the trick, you will have to replace the fan module under the steering column. It's a little black box that unplugs and pops off a holder.