X2, there isn't much to them, thats why you're going with a cheap square shaft and not a nice round one...take a piece of square tubing about 2 in. find another piece that fits nicley inside of that.
take your driveline now.
cut the ends off (at about the weld)
weld one end on to the 2 in tube
weld the other end to the smaller diameter tube.
take the measurment from the t case to the pinion and make sure your drivelin is that length plus about 5 in.
and bada bing bada boo you have a square drivline!!