I went to start my '67 Mustang yesterday after its been sitting for a few months and it just makes a winding noise (or spinning noise) like a drill. It sounds like it's coming from the front passenger side. It does not try to turnover, just this wind up and then once turned off a wind down. What should I be looking for as a possible issue? Thanks in advance.

 

I'd say your starter isn't engaging. From what I recall the starter is on the passenger side. And the spinning noise is the starter spinning up, but it isn't moving to the flywheel to turn the engine over.

 

Our Mustang starters only have the one large positive cable to the starter, the starter relay being up on the inner right fender. There is not a lot that can be done to troubleshoot the Bendix drive that isn't simpler than just replacing the starter. Any troubleshooting would require you to remove and reinstall the starter anyway. It is possible that the Bendix drive has failed, or the integral solenoid is not functioning. I don't see that you can service the solenoid anymore (without replacing it with a new starter), but the Bendix drive is readily available. If you decide to replace the starter, get the best you can afford. The inexpensive remanufactured ones are more likely to have this same problem occur again.
In the meantime, it is possible things are just gummed up and the Bendix could free itself if you just try to start it a few more times. This is obviously not the most reliable thing to do, and if it does start working, you'd be gambling on when it would fail again and where.