Beats of Rage is not really that big in size. The biggest file sizes (1MB or more) comes from the background music that is mostly WAV file converted to BOR.
Most character sets are around 100KB
Levels can be between 100KB to 200KB
Intros in BOR are animated GIFs, can be converted to IFF ANIM files
Sound FX are WAV, can be IFF
The game can be small, if someone could code it.
I used to mod BOR with my friend about 10 years ago, I would love to port our mod to the Amiga.