Would an old 302 motor fit in a 1989 Ford Mustang LX 4-cylinderinder?

No, a 302 (5.0L) V8 engine will not fit in a 1989 Ford Mustang LX 4-cylinder without significant modifications. The 4-cylinder Mustang has a much smaller engine bay. You'd need to modify or replace the firewall, possibly the radiator support, and likely the suspension components to accommodate the larger V8. It's a major undertaking, far beyond a simple swap.