Thanks for the feedback. Your comment about the Jeep IS made me so curious that I forked out the money and bought a brand new 10 spline Jeep T5 IS. The number of IS gear teeth (21) is the same as the S10. On the bench it appears to be a great solution and the splines on the Jeep IS are cut further along the shaft than the S10.
Remove the S10 IS and replace it with the Jeep IS. Cut the Jeep IS to the proper length and then the bearing retainer too. The original clutch disc and friction plate from my original Saginaw will work (but a new one will be installed).
3 shafts side by side The Jeep IS has longer splines. Jeep IS fits 1965 clutch disc
