Just remove the 4.0 Dev Build from the Gamedata file if you have it installed. Then install the 3.3.4 version the way you normally did in the older versions of KSP. That is, put the parts in the Parts folder and Plugin and PluginData in their appropriate folders. The only issue I ran into was when I started mapping, I received the "no terrain detected screen" instead of the black screen. Once I started mapping it worked normally and it will map over that screen. I have used version 4.0 and it's a great version, but not everyone can run it if they use a lot of mod parts. This is just an option for those people.