I wouldn't screw with your tranny, if they welded on the shaft I'm sure that the metallurgy is screwed up. 1988 used a clip, stay away from those that use a nut on the sprocket, i've heard that you can't get the nuts anymore. Newer would be better, some used trannys had the drive cogs rounded causing them to jump out of gear. not only are the shafts different the clutches (clutch splines, some had 5 springs the newer had 6) are different in the 87 and older, can't remember if 88 is same or newer. Have you thought about replacing the shaft?