Are you referring to the 2010 GT 500 or the 2010 GT? I have a 2010 GT and just installed a GT 500 fuel pump this weekend with the only issue being the wiring for the fuel gauge...so I don't understand what you mean by a different fuel sender unit..?
The 2010 GT and GT500 both use a different fuel level sender than the previous 05-09 did. What will happen if you use a 05-09 level sender on your car such as the one included in FRPP GT500 fuel system # M-9407-GT05 is that your fuel level sender will not register the fuel reading correctly. It's almost like the 2010 does the opposite as the 05-09 does. If you fill the tank the level reads low. When you run low on fuel the level reads high.
There's a separate part number for 2010 cars that want to run the FRPP GT500 system which is M-9407-MSVTA. Here's the note the have on their site as well.
Note: Use of this kit in a 2005-2009 Mustang will result in an incorrect fuel gauge reading.
Thanks for the info...sigh...need to find someone with a 2010 GT 500 to swap with...or just live with an opposite fuel gauge...hmmm...so....if I swap the F and the E it will be right, problem solved!