Type, Field, Method, Extends, etc.
Under Blitz II you have Arrays, Lists and NewTypes (can't remember anything else), you could probably convert most stuff from BlitzMax to Blitz II, but it's more complicated if the BlitzMax code includes stuff like inheritance and methods.
If the code you have works in Blitz3D or Blitz2D (also known as Blitz Basic PC) then it should be far easier to convert.