So it's already available for MorphOS and OS4? I didn't know, but that's good.
About running it on classic Amigas, i don't think it's a problem about using more or less colours, most of the ports are just 256 colours, that would just need an AGA machine.
However, more than probably the engine would need to be adapted to the 68k architecture, once done i do believe a 030 could do the task fairly.
Weren't some guys here trying to develop new games for the classic Amigas? It would be a good idea if they take a look to the project.