Can I just buy a clutch that matches the S10 spline count and trim the S10 input shaft?
Yes, that's what I did. Since I have an 11 inch clutch/pressure plate, etc I had to hunt a bit but it is all out there. I think I ended up buying a LUK pressure plate, clutch disc and the short throw-out bearing. You can trim the end. I didn't have to since my T5 came from an Astro Van and it was ok on length.