> I notice that some of the source code was release several years ago, though
> it doesn't seem to have been taken up by anyone in the interim. I took a
> quick look at it but couldn't find anything related to the game engine itself.

Exactly. This source code was released even before the Amiga port of Shogo was started.

> Alternatively, I notice that there's a Mac port as well.

Btw, this Mac port was done by the same company as the Amiga port (as well as the Linux port).