360 Magnum with stock EFI engine codes

There are several reason. Many deal with lazy, lack of time, and lack of knowledge. I’m a long way away from calling it done. I’m going to work on putting an H pipe in and plan to put the first O2 sensor in it. My lack of knowledge kicks in by not knowing whether to us an o2 sensor from an automatic or a manual since the trans is not hooked to the computer. Also the wiring issue. I don’t believe I have any unused plugs in the wiring harness from the PCM to the fuse box. So I’m guessing I need to run wires for the O2 sensor, but not sure where. Next question is if I put in a post cat O2, where do I put it since I don’t have catalytic converters. If I don’t put the second O2 in, is there a way to work around it?