Welcome to the community. We have a section devoted to vintage builds > http://motorbicycling.com/forumdisplay.php?f=38
You might find some good information regarding your plans to build a Harley replica.
Just a suggestion but you might want to explore building a simple motorized bicycle first so you get some experience and see what is involved. Building a replica for a first project is possible of course depending on your fabrication and metal working skills but starting out simple first will provide you with insight into what will be required to build a reliable and successful bike.