You just take the source and run it with Rebol. Shold work just like that. Amiga version of Rebol don't yet have -executable compiler so there is no amiga-specific runable code. Unfortunately I have this feeling that on Amiga it'll be a bit slow, but...
Note: that source is actualy bit obfuscated.. In a way pitty cause it would have been nice introduction to those who like to see more of Rebol.