Re which will work, all the Saginaw gears have the same bolt pattern. Some are 3-bolt, some 4-bolt. The 3-bolt just eliminates one of the bolts in the pattern - you can use a 4-bolt gear with the 3-bolt bracket, or a 3-bolt gear with a 4-bolt bracket, or match 3 with 3 or 4 with 4. The manual gears are all 3-bolt AFAIK.
The input shaft diameters change, but the proper bell coupling is all that's needed to match the shaft to the gear. Available aftermarket. I expect easiest for you would be the CJ power gear same year as your manual gear.
The CJ OEM gears are 4-bolt, and the S10 gears are 3-bolt. The CJ input shaft is larger, but the S10 input is the smaller size, matching the CJ manual gear.