I agree with Tommy, The only advantage is for drag racing because it would be lighter [smaller gear box, no pump, hoses or fluid] and less strain on the motor from the pump. For the street, it would give you problems in tight manuvers.

As for years, it looks like they were only in 82-84 2WD S-10s with 4 cylinders and 78-79 Malibus. I do believe the pitman arm splines are differant between the power and manual gear boxes, so you'll have to find a new pitman arm as well.