There will probably be a lot of fine sand in everything from the water. Can you work on the vehicle where it's at now, when it is dry? I wouldn't worry a whole lot about rust and corrosion. If you can get the vehicle on dry land and begin the disassembly process as soon as possible for inspection, rust should not be an issue. I have seen guys take apart entire Mack 10 ton trucks and rebuild them in a years time. Don't worry about the electrical bits, electrical is easy and small potatoes. Yank the entire drive drain and service everything. It will be labor intensive and time consuming, just take your time and keep in mind the truck will look brand new when you are finished with it. After all, with the entire vehicle disassembled it will be a great excuse to put all new paint on everything. You figure the drivetrain components will have so much diesel oil, gear oil, grease (etc) on them that rust on the internals probably won't be a big problem. If there is any rust on the internals it will likely be minor surface corrosion at best, and can be cleaned up easily with no need to replace the parts.