Two things to watch out for. First is the obvious narrower track. Many people use this to their advantage so they can run "deep dish" wheels on the back. Personally I like the look of a lot of offset on a rim, but you can make the tires fit with the correct offset and the original axle. The second thing is the pinion flange to axle centerline dimension. The various GM axles have different dimensions here that can require differences in driveshaft length. If the driveshaft is too short it can fall out of the trans output shaft (or at least leak trans fluid) and if it's too long you'll damage the pinion bearings.
Don't ask me how I know this...
