Exactly my 65 Barracuda has a 8.25 rear put in it to replace the original small rear end. Just as stated the driveshaft needs to be adjusted, but it is perfect time to make it more modern and put in a modern u-joint set up also to replace the ball and trunion set up. Mine was done that way and no issues what so ever, in fact had done it before on a previous project 66 Barracuda I drag raced with a 8.75 rear that was built for it. That in fact was narrowed to fit. I drive it all the time and love it mine has 14" mopar rally wheels on it with nice tires. The back ones just a little wider than front!
65Cudalover