Well crap, that went downhill in a hurry.
To avoid permanent damage, you need to get to it ASAP after the water recedes. Pull the trans and engine drain plugs and let all the water out. You'll need to drain the fuel tank too.
Pull the spark plugs and roll the motor over until water stops coming out. Refill the crankcase and dump a bunch of oil down the plug holes and roll it a bit more. Any oil will do, you just want to get the cylinders coated. Then get the dang carb on it and get it started ASAP!!
Assuming it's fresh water, the wiring will be fine once it dries, but gauges may no longer work. I would unhook them until they drain/dry out. Drill a hole in the bottom if necessary to let any trapped water out. Don't put power to them until they are GOOD and dry. They might work...
If you can't get it running right away, then fill the engine/trans both with diesel fuel, right to the top. That'll at least keep things from rusting more, and it'll help keep any rust that did happen from becoming an issue...
Man, it's a day of work, but if you can get to it quickly, it'll keep your tractor from becoming scrap...
Good luck!!