Will a 2.3 liter motor out of 91 Mustang fit right in an 89 Ranger?

No, a 2.3L engine from a 1991 Mustang will not fit directly into a 1989 Ford Ranger without significant modifications. While both are Ford products and use the same basic engine family (the Lima engine), the mounting points, accessories (alternator, power steering pump, etc.), and potentially even the bellhousing for the transmission will be different. You'd be looking at a substantial engine swap project requiring custom fabrication and potentially significant expense.