Guys, he apparently has flanges that match on all ends as the DS's are bolted into place and functional. His question is how to determine if the shaft lengths are correct and whether he needs longer or shorter DS's.
Look at a stock rig and determine how much spline is showing on the slip joint. My guess is the 1" to 1.5" is probably about right. Put tape on the shaft right where the 2 ends meet up on the splines. Then pull the shaft apart and measure how much spline you have on the inside. That will give a rough idea of whether you are centered up or too deep/shallow.
Randy Rosetta KDØKWX TLCA #19351 69 FJ40 "Meanie" & 1970 Boss 302 Mustang