Why doesn't my 410 bolt 3 shot model 58 have a safety?

Your model 58 .410 may have a safety after all. Look at the end of the bolt and see if there is a 'notch' that the 'knob' of the bolt can be pulled and turned until it catches in the notch. I have had several guns designed this way; but, yours may not be. Go the Numrich Gun Parts Corp. website and find the diagram for your model 58. If yours has a letter after the 58, be sure to get the right diagram. There are several different ones. Hope this helps.