The oem bolts have a dog point that fits with a tight fit into a hole in the block past the threads, this coupled with a very large shoulder locate the bracket. Believe me I found out the hard way, breaking non oem bolts off in the block launching the car. If the bracket had dowels to locate it, it wouldn't matter what bolts are used, like a 3000gt axle bracket.
To make it simple, the oem bolts act as dowels, and bolts. To just use regular bolts, you have no dowels.