No, a standard 305 cubic inch small-block Chevrolet engine (like the ones found in many Chevy cars and trucks) cannot be directly swapped into a Chevy Astro van without significant modifications. The Astro van used a different engine bay layout and mounting points compared to vehicles that typically housed a 305. You'd have to fabricate custom engine mounts, likely modify the firewall, and address exhaust and other systems. It would be a very extensive and complex project.
While not impossible, the amount of work involved would likely exceed the cost and effort of finding a suitable used engine of a type compatible with the Astro's chassis.
