If you want to get an idea if the rear gears have been changed there is an easy way. Jack up the back of the car so both wheels are off the ground. Be sure to use jack stands. Put the tranny in neutral only after blocking the front wheels so the car doesn't shift. Mark a line on your driveshaft...
Barracudas are nice cars. I still have the one I ordered new in 1972. Reading all the comments above, I agree that if that car is not his "dream car" then maybe it is not the right one.
If you draw an imaginary line down from the trunk key cylinder it appears to be lined up with the bumper. Moving the emblem should be no big deal. I would have done it already if it was my car.
I don't think you can put the tapered axles in the newer housing. I'm pretty sure you need to replace the housing to do this. I put a complete housing in my 57 in the sixties. I ended up using an axle that was a little narrower and just relocated the spring perches.