Go to this web page for details:
http://www.willegal.net/appleii/appleii-kb-int.htm

In my opinion, building one of these adapters is not very difficult. I have been able build and test one of these adapters in about an hour.

If you can get a piece of Apple 1 software into Apple Monitor Command format, I believe that this RS232 interface is one of the most straight-forward ways to download software from a PC to your Apple 1.