I just purchased a 2006 Heritage that was lower than I thought it should be. How can I tell if the dual shocks are stock or are a (lowered) set?

 

The shaft towards the front of the shock housing is lengthened if the bike has been lowered, pre 2018 Softail is kinda backward, longer the shock the lower the bike.
You could try a Google image search, or you tube for more on this. Good luck, ride safe.