* Ford 8.8-inch: This was a very common and popular axle in many Ford trucks and Broncos of that era. It's a durable and relatively easy-to-work-on axle.
* Dana 44: Less common than the 8.8, but some higher-spec Broncos, particularly those with four-wheel drive and off-road packages, might have had a Dana 44 rear axle. The Dana 44 is known for its strength and capability.
To know for certain what rear axle is in *your* specific 1989 Ford Bronco, you'll need to check the vehicle's identification number (VIN) or look at the axle itself. The axle housing usually has a casting number that will identify it.