01 chevy s-10
any small block chevy V8 will "fit". The engine computer controls the gauges and A/C, so to keep these features, the easiest (yet most expensive) is an LSX motor because companies sell wiring harness' that plug into that truck. The harness adapts the V8 motor computer to the rest of the truck so everything works.
Have you thought of modding the 4.3? If you go to www.s-seriesforum.com, there is a performance forum there. In there, there are guys that have built naturally aspirated 4.3's that run good, and turbo or supercharger trucks that are running great.