I'm trying to access my site on the dev box via https and I'm getting a 404 - 443 is configured correctly - this is a 2008 r2 box with iis 6.1.
application runs fine on local box - where should I start looking ?
404 is page not found. So the port is open and the 443 is going through fine. Make sure the file you are trying to hit is in the location you're trying to reach.
As San mentions, 404 is a file not found error.
Check your IIS configuration and ensure the file/index you are requesting exists within the configured directory.
Something like this may assist, http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/a59a2665-9078-43ef-8b5a-5bf9bcacc95e.mspx?mfr=true