The Astro van uses a 4.3L V6 engine with a 4-speed automatic transmission, while the S10 pickup uses a 2.2L inline-4 engine with a 5-speed manual transmission. The engines have different mounting points and bellhousings, so they will not bolt up to each other.
Additionally, the transmissions have different bolt patterns and spline counts, so they will not mate up to each other.
Therefore, it is not possible to swap the engine and transmission from a 1995 Chevy Astro van into a 1999 S10 pickup.