Will a 95 s-10 transmission fit in your 95 blazer?

Yes. Either you have an NV3500 (if it's a manual) or a 4L60E (if it's an automatic)... however, if one is 2WD and the other is 4WD, they won't be compatible, as the 2WD transmission will have an output intended to go directly to the driveshaft, and the 4WD transmission will have an output intended to go into a transfer case, plus a different mounting service intended for the transfer case.