I believe alll the 300 SE's from '88-'91 had markings on both shafts that identified where to interface them. One shaft had an embossed arrow, and the other had two arrows spaced a bit apart. Just center the one arrow between the other two, and you have the correct splines aligned. Assuming the shafts you have are matched and balanced this way to begin with - a rebuilt and re-balanced shaft set may not be, but should be if a good shop did the rebuild.

DG