Will a cavaleir engine fit in S10?

No, a Cavalier engine will not fit in an S10 without significant modifications, and it's highly unlikely to be practical or worthwhile. The Cavalier (and its related models like the Sunfire) used smaller, transversely mounted engines, while the S10 typically used a larger, longitudinally mounted V6 or inline-4 engine. The engine bay dimensions, mounting points, and accessory placement are completely different.