In my opinion, for the types, go with optional. Maybe "// @param param[: string] some value". For bonus points, type inference (if you see a value used as an object, it's probably an object, if you pass it to something you know takes a string, it's probably a string, etc)!
On another note, what would the point of running this from within Blockland be? I'ts just a tool you run before releasing, not while developing or as a user, would be it would be useful if you could have a travis/jenkins job do it automatically.
For the private stuff,
Scaladoc handles that pretty nicely.