Just Flight has posted on Facebook further previews of their upcoming Boeing 747 Classic. The previews show the aircraft departing from JFK airport, and showcases the use of what appears to be GSX jetways. In the comments, Just Flight further reiterated the Boeing 747-300 was planned but at a later stage in an expansion pack.
You can visit the product page at Just Flight website for more information regarding the expected features of the Just Flight Boeing 747 Classic.