What issues would I have going to a 9"?

If your not changing your tranny I don't think you'll have to shorten your drive shaft. Is it the right width? If not you'll have to have the axel tubes shortened.

first check the bolt pattern on the 9" housing ends. if they match the 8" ends you are good to go on using the backing plates from your 8". next check the width of the axle, again if they are the same you can use the axles. you then need to use a 9" center section that has 28 spline axles, but are the small 28 spline axles, yes there are two different sizes of 9" 28 spline side gears. as far as shortening your driveshaft, maybe. the 9" center section is longer than the 8" by almost 5/8", and the input yoke is usually longer as well.

Doesn't the 9" have the brake assembly on it? If so ,just use them. I went from a six cyl. rear to a 9" and the driveshaft worked fine.