Can you put a 350 Chevy engine in 1985 s10 blazer without changing transmissions?

No, you almost certainly cannot put a 350 Chevy engine in a 1985 S10 Blazer without changing the transmission. The stock transmission in a 1985 S10 Blazer was not designed to handle the torque of a 350 cubic inch V8. You'd risk serious and potentially catastrophic transmission failure. You'll need a much more robust transmission, like a TH350, TH400, or a 700R4 (with modifications likely needed for the 350's torque).