If your thinking about swapping in a 9.75 in the rear, it should be a direct bolt-in, as long as it comes from an 04-up F-150. the only thing that might cause a problem is the driveshaft length.

I once did a very similar swap, I had an 87 T-bird with a 5.0L and the factory rear axle was a 7.5" (the same one that was behind a four banger in the pinto) way too small for a 3800 pound car with a V-8. So I put in an 8.8 out of an 88 stang and it was a direct fit.

 

8.8's can be tough rear ends. I actually wouldnt mind swapping an 8.8 in my 04 over my 9.75. Alot lighter rear end and shouldn't rob as much power.

 

Should theoretically be very simple/easy swap.

Find a junker at the local junk yard, jack up the truck, remove drive shaft, unbolt rear end from u-joints and take it home..

8.8 would do ya fine though.

 

I believe you correct

I have the 8.8. I run hell out of my truck and I haven't had any problems as of yet (knock on wood). If you have any other questions let me know.