you need at least 1 degree of difference at each u-joint so that they move some to keep them from vibrating, keep the angles as close to the same as possible also keep all the joints aligned on the shaft. if you take the slide splines apart, mark everything so that you can reinstall it in the same orientation. use a simple angle guage from sears or harbor freight, just check it for accuracy by taking a reading and then turn it 180 deg and take another reading they should be the same. just take your time and get the angles right. the first install/measurement operation will probably not be the winning ride at this rodeo, just plan on adjusting the carrier bearings a couple of times and don't let yourslf get frustrated.